What is the best organization of a child’s day to maximize bone health and function in children?

Not too little, not too much – Goldilocks’ “just right” approach can now assess children’s daily activities as new research from the University of South Australia confirms the best make up of a child’s day to maximize bone health and function in children.

Examining 804 Australian children aged between 11 and 13 years old, the world-first study found that children need more moderate-to-vigorous physical activity, more sleep and less sedentary time to optimize bone health.

The study found the ideal balance of a child’s activities across a 24-hour period comprises:

1.5 hours of moderate-to-vigorous physical activity (sports, running around)
3.4 hours of light physical activity (walking, doing chores)
8.2 hours of sedentary time (studying, sitting at school, reading)
10.9 hours of sleep.
Lead researcher, UniSA’s Dr. Dot Dumuid say that the findings provide valuable insights for parents, caregivers and clinicians.

“Children’s activities throughout the whole 24-hour day are important for their bone health, but until now, we haven’t known the perfect combination of exercise, sleep and sedentary time,” Dr. Dumuid says.

“Higher levels of physical activity are known to be good for children’s bone health, yet we can’t just increase children’s exercise without impacting their other activities.

In this study, we looked at the interrelating factors of physical activity (both light, and moderate-to-vigorous physical activity), sedentary time and sleep, finding an ideal combination that delivers the best daily balance.

The ‘Goldilocks Day’ tells us the durations of physical activity, sleep and sitting that are ‘just right’ for children’s optimal bone health.”

Up to 90 percent of peak bone mass is achieved by age 18-20, which makes this especially important during childhood and adolescence.

Optimizing bone health in children is a key protector against osteoporosis, the leading preventable cause of fracture in adults and a major public health problem with considerable economic and societal costs.

Osteoporosis is common in Australia, with 1.2 million people estimated to have the condition and a further 6.3 million with low bone density. Globally, osteoporosis affects 200 million people, with 75 million cases across Europe, U.S. and Japan.

In this study, participants were selected from the Child Health CheckPoint study within the Longitudinal Study of Australian Children. Activity data was collected through accelerometer readings (worn for 24 hours a day over an eight-day period), supplemented by self-recorded logs for bed and wake times.

Bone measures were recorded via peripheral QCT scans of the leg (ankle and shin) to identify bone density and geometric parameters.

Dr. Dumuid says the study also highlights the importance of sleep, especially for boys.

“We always talk about getting enough exercise to help build bones, but for children, it’s vital that they also get enough sleep. Curiously, the study also showed that sleep is more important for boys’ bone health than for girls, with boys needing an extra 2.4 hours of sleep a day.

However, boys tended to be at earlier stages of pubertal development than girls, causing us to speculate that the need for longer sleep is related to rapidly changing hormonal processes rather than gender.

By knowing the best balances and interrelations of sleep, exercise and rest, parents and caregivers can guide their child’s daily activities to put them in good stead for future bone health.”

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Key Messages

• There is much that individuals can do to promote their own bone health, beginning in childhood and continuing into old age. These activities contribute not only to bone health, but to overall health and vitality.
• Since many nutrients are important for bone health, it is important to eat a well-balanced diet containing a variety of foods, including grains, fruits and vegetables, nonfat or low-fat dairy products or other calcium-rich foods, and meat or beans each day.
• Most Americans do not consume recommended levels of calcium, but reaching these levels is a feasible goal. Approximately three 8-ounce glasses of low-fat milk each day, combined with the calcium from the rest of a normal diet, is enough to meet the recommended daily requirements for most individuals. Foods fortified with calcium and calcium supplements can assist those who do not consume an adequate amount of calcium-rich foods.
• For many, especially elderly individuals, getting enough vitamin D from sunshine is not practical. These individuals should look to boost their vitamin D levels through diet. Vitamin D is also available in supplements for those unable to get enough through sunshine and diet.
• In addition to meeting recommended guidelines for physical activity (at least 30 minutes a day for adults and 60 minutes for children), specific strength-and weight-bearing activities are critical to building and maintaining bone mass throughout life.
• Individuals should see a health care provider if they have a medical condition or use medications that can affect the skeleton. Women should also see their health care provider if menstrual periods stop for 3 months.

As the evidence presented in the previous chapter makes clear, there is much that individuals can do to promote their own bone health throughout life. This chapter outlines recommendations for diet, physical activity, and other lifestyle practices that can help to achieve that goal.

Moreover, the activities and practices suggested in this chapter contribute not only to bone health, but to overall health and vitality. In fact, bone-specific recommendations fit well within an overall program of good nutrition and physical activity that should be followed in order to prevent the onset of many of the major chronic diseases affecting Americans.

Nutrition

Since many nutrients are important for bone health, it is important to eat a well-balanced diet containing a variety of foods. Following the Dietary Guidelines for Americans (USDA 2000, USDHHS 2000) can help, although attention should be paid to serving sizes. These guidelines urge individuals to eat 6–11 servings of grain foods, 3–5 servings of vegetables, 2–4 servings of fruits, 2–3 servings of dairy or other calcium-rich foods, and 2–3 servings of meat or beans each day.

The DASH (Dietary Approaches to Stop Hypertension) Eating Plan (USDHHS 2003), which follows these guidelines, is an example of a well-balanced diet that can be good for bone and heart health, although bone outcomes from DASH have not been specifically tested.

The DASH Eating Plan emphasizes fruits, vegetables, low-fat or fat-free dairy foods, whole grains, fish, poultry, and nuts, making it rich in calcium, magnesium, protein, and potassium while also being low in fat, cholesterol, and sodium. For more information about the Dietary Guidelines and the DASH Eating Plan, refer to Appendix C, Resources and Related Links.

Calcium

The Food and Nutrition Board (FNB) of the Institute of Medicine updated recommended intakes for several nutrients important to the skeleton in 1997, including calcium (IOM 1997). Recommended amounts of calcium, which are shown in Table 7-1, differ by age. These recommendations are meant for healthy people.

Those with osteoporosis or other chronic conditions may need more calcium, but unfortunately the calcium requirements for individuals with this disease have not yet been clearly identified (Heaney and Weaver 2003).

The highest amount (1,300 mg per day) is recommended for children and adolescents ages 9–18, a period when bones are growing rapidly.

Pregnant or lactating women are advised to consume an age-appropriate amount of calcium, as shown in Table 7-1. The Institute of Medicine also defined a safe upper limit of 2,500 mg per day for calcium (IOM 1997).

Intakes above 2,500 mg per day may increase the risk of adverse effects in susceptible individuals.

Table 7-1Adequate Intakes (Al) or Recommended Dietary Allowances (RDA) and Tolerable Upper Intake Levels (UL) for Calcium, Vitamin D, Phosphorus, and Magnesium by Life-Stage Group for United States and Canada

Life-stage group	Calcium (mg/day)	Vitamin D (IU/day)	Phosphorous (mg/day)	Magnesium (mg/day)
	Al	UL	Al	UL	RDA	UL	RDA	UL†
Male	Female
0–6 months	210	ND*	200	1000	100	ND*	30	30	ND*
7–12 months	270	ND*	200	1000	275	ND*	75	75	ND*
1–3 years	500	2500	200	2000	460	3000	80	80	65
4–8 years	800	2500	200	2000	500	3000	130	130	110
9–13 years	1300	2500	200	2000	1250	4000	240	240	350
14–18 years	1300	2500	200	2000	1250	4000	410	360	350
19–30 years	1000	2500	200	2000	700	4000	400	310	350
31–50 years	1000	2500	200	2000	700	4000	420	320	350
51–70 years	1200	2500	400	2000	700	4000	420	320	350
> 70 years	1200	2500	600	2000	700	3000	420	320	350
Pregnancy:
<18 years	1300	2500	200	2000	1250	3500		400	350
19–30 years	1000	2500	200	2000	700	3500		350	350
31–50 years	1000	2500	200	2000	700	3500		360	350
Lactation:
<18 years	1300	2500	200	2000	1250	4000		360	350
19–3 years	1000	2500	200	2000	700	4000		310	350
31–50 years	1000	2500	200	2000	700	4000		320	350

mericans obtain most of their calcium from dairy products. In fact, approximately three 8-ounce glasses of milk each day, combined with the calcium from the rest of a normal diet, is enough to meet the recommended daily requirements for most adults. Lowfat or nonfat versions of dairy products are good choices because they have the full amount of calcium, but help to avoid eating too much fat.

Foods that have been fortified with calcium are also good sources of the nutrient. There are many foods that serve as good sources of calcium, including fortified cereal, nonfat milk, and calcium-fortified orange juice from frozen concentrate (Keller et al. 2002). Vegetables also contain calcium, but the amount of calcium absorbed from these sources varies; some, like broccoli and kale, contain calcium that is well absorbed, while others, such as spinach, do not (Weaver et al. 1999).

It would be impractical for most people to eat enough vegetables or other low-calcium foods to meet recommended levels if these were the only sources of calcium in the diet. To assist in planning a diet containing adequate levels of calcium, Table 7-2 provides a list of selected food sources of calcium, along with the percent daily value that they contain.

These percentages indicate whether a serving of the food contains a high (20 percent or more of the percent daily value) or a low (5 percent or less) amount of a specific nutrient—in this case, calcium. Most individuals can design a diet that is appealing to them (based on their preferences) while also meeting their nutrient needs.

Table 7-2Selected Food Sources of Calcium

Food	Calcium (mg)	% DV*
Sardines, canned in oil, with bones, 3 oz.	324	32%
Cheddar cheese, 1½ oz. shredded	306	31%
Milk, nonfat, 8 fl oz.	302	30%
Yogurt, plain, low fat, 8 oz	300	30%
Milk, reduced fat (2% milk fat), no solids, 8 fl oz.	297	30%
Milk, whole (3.25% milk fat), 8 fl oz.	291	29%
Milk, buttermilk, 8 fl oz.	285	29%
Milk, lactose reduced, 8fl oz. (content varies slightly according to fat content; average = 300 mg)	285–302	29–30%
Cottage cheese, 1% milk fat, 2 cups unpacked	276	28%
Mozzarella, part skim 1½ oz.	275	28%
Tofu, firm, w/calcium, ½ cup†	204	20%
Orange juice, calcium fortified, 6 fl oz.	200–260	20–26%
Salmon, pink, canned, solids with bone, 3 oz.	181	18%
Pudding, chocolate, instant, made with w/2% milk, ½ cup	153	15%
Tofu, soft, w/calcium, ½ cup†	138	14%
Breakfast drink, orange flavor, powder prepared with water, 8 fl oz.	133	13%
Frozen yogurt, vanilla, soft serve, ½ cup	103	10%
Ready to eat cereal, calcium fortified, 1 cup	100–1000	10%–100%
Turnip greens, boiled, ½ cup	99	10%
Kale, raw, 1 cup	90	9%
Kale, cooked, 1 cup	94	9%
Ice Cream, vanilla, ½ cup	85	8.5%
Soy beverage, calcium fortified, 8 fl oz.	80–500	8–50%
Chinese cabbage, raw, 1 cup	74	7%
Tortilla, corn, ready to bake/fry, 1 medium	42	4%
Tortilla, flour, ready to bake/fry, one 6″ diameter	37	4%
Sour cream, reduced fat, cultured, 2 tbsp	32	3%
Bread, white, 1 oz.	31	3%
Broccoli, raw, ½ cup	21	2%
Bread, whole wheat, 1 slice	20	2%
Cheese, cream, regular, 1 Tbsp	12	1%

Many individuals, especially non-Whites, suffer from lactose intolerance. These individuals may avoid dairy products, which can result in a low calcium intake unless other good sources of calcium are consumed. Those with lactose intolerance may develop the capability to digest lactose if they slowly build up milk intake over a period of days or weeks so that they develop an intestinal flora capable of digesting milk’s lactose (Suarez et al. 1997). Many lactose-intolerant individuals can tolerate up to one cup of milk twice a day if it is consumed with food (McBean and Miller 1998). In addition, some other calcium-rich dairy products such as cheese and yogurt are usually well tolerated by lactose-intolerant people. Finally, there are a number of calcium-rich foods that do not contain lactose, including lactose-free milk, fortified soy beverage, and fortified juice and cereal. Some tips for those with lactose intolerance are shown in the box below.

A Guide to Calculate Calcium Intake

As shown in Figure 6-4 of Chapter 6, most Americans above age 9 on average do not consume recommended levels of calcium. The following guide allows an adult to compare a rough estimate of his or her intake of calcium to the recommended amounts:

• Start by writing down the following amount:
  • ~ 290 if you are a female, regardless of age, or male age 60 or older
  • ~ 370 if you a male under age 60

This is the average amount of calcium that most people eat from non-calcium rich food sources (Cook and Friday 2003, Wright et al. 2003, Weinberg et al. 2004).

• Add 300 mg for each 8-ounce serving of milk or the equivalent serving of other calcium-rich foods (e.g., yogurt, cheese).
• For those taking a calcium supplement or a multi-vitamin containing calcium, add the amount of calcium from that source:
  • ~ Check the supplement label for the amount of calcium per supplement dose.
  • ~Multiply the amount per supplement dose times the number of doses taken each day.
  • ~Add the amount from supplements to the base amount and the amount from calcium-rich foods.
• Compare this rough estimate of total calcium intake to the recommended levels shown in Table 7-1. Individuals should try to meet their recommended level of calcium on most days.
• A useful calcium calculator for children can be found at: http://www.cdc.gov/powerfulbones/parents/toolbox/calculator.html.

Tips for Those With Lactose Intolerance

• Choose dairy and other calcium-rich foods with lower amounts of lactose; a list of the amount of calcium and lactose in common foods is shown in Table 7-3:
  • ~ Yogurt with live active cultures (which provide bacterial lactase that digests the lactose).
  • ~ Hard cheeses like cheddar, Colby, Swiss, and Parmesan (the production process for these cheeses breaks down the lactose).
  • ~ Lactose-free or lactose-reduced products, including milk without lactose.
• Gradually increase the amount of lactose-containing foods consumed.
• Consume non-dairy products that contain high levels of calcium, such as fortified soy beverage or fortified cereal or orange juice.

(Jarvis and Miller 2002)

Table 7-3 Calcium and Lactose in Common Foods

	Calcium Content	Lactose Content
Vegetables, Fruit, Seafood
Calcium-fortified orange juice, 1 cup	308–344 mg	0
Sardines, with edible bones, 3 oz.	270 mg	0
Salmon, canned, with edible bones, 3 oz.	205 mg	0
Soymilk, fortified, 1 cup	200 mg	0
Broccoli (raw), 1 cup	90 mg	0
Orange, 1 medium	50 mg	0
Pinto beans, ½ cup	40 mg	0
Tuna, canned, 3 oz.	10 mg	0
Lettuce greens, ½ cup	10 mg	0
Dairy Products
Yogurt, plain, low-fat, 1 cup	415 mg	5g
Milk, reduced fat, 1 cup	295 mg	11 g
Swiss cheese, 1 oz.	270 mg	1g
Ice cream, ½ cup	85 mg	6g
Cottage cheese, ½ cup	75 mg	2–3 g

The Institute of Medicine recommends that nutrients be obtained from food when possible because they provide a package of nutrients that are good for other tissues besides bones. However, fortified foods and supplements can assist those individuals who do not consume an adequate amount of dairy products or other naturally calcium-rich foods to meet recommended levels of calcium intake.

Those who take supplements or consume fortified foods should note that: a) all major forms of calcium (e.g., carbonate, citrate) are absorbed well when taken with meals; b) calcium from supplements or fortified foods is best taken in several small doses (no more than 500–600 mg at one time) (Heaney 1975) throughout the day for better absorption; and c) supplements may differ in their absorbability due to manufacturing practices (IOM 1997).

One need not choose the most expensive products on the market, as the cost of supplements of comparable quality can vary fivefold (Heaney et al. 2001). In a recent evaluation of calcium sources, calcium carbonate supplements were found to be the least expensive supplemental source of calcium. Since virtually all calcium sources—food or supplement—reduce the absorption of iron, calcium and iron supplements should be taken at different times.

Vitamin D

The current recommended intakes of vitamin D are given in Table 7-1. Most individuals need 200 IU per day, although these recommendations are raised to 400 IU per day in those age 50–70, and to 600 IU per day in those over age 70. There are two sources of vitamin D: sunlight and dietary intake.

As discussed in Chapter 6, vitamin D can be made in the skin by being exposed to sunlight.

For some individuals, particularly children and others who get enough exposure during warmer months, the sun can provide adequate levels of vitamin D throughout the entire year. For many, however, it is not practical to get adequate levels of vitamin D from exposure to sunshine.

These individuals should instead look to boost their vitamin D levels through diet. This is especially true for elderly individuals who have higher vitamin D needs and who may have difficulty getting outside everyday.

People with dark skin and those who live in areas with heavy air pollution may also find it more practical to obtain most or all of their vitamin D from diet, since they need longer periods of sun exposure to get adequate levels of vitamin D. Table 7-4 gives the vitamin D content of several foods, although the most common source is fortified milk.

One cup of fortified milk contains 100 IU vitamin D, half of the recommended intake for individuals under age 50. Since vitamin D-fortified milk is not used when making cheese, ice cream, or most yogurts, many other dairy foods are not good sources of vitamin D.

Other good dietary sources of vitamin D include fatty fish and vitamin D-fortified orange juice. The best way to know whether a dairy food contains vitamin D is to check the nutrition label.

Table 7-4 Dietary Sources of Vitamin D

	Serving Size	Vitamin D (IU)
Milk	1 cup	98
Baked herring	3 oz.	1,775
Baked salmon	3 oz.	238
Canned tuna	3 oz.	136
Sardines	1 oz.	77
Raisin bran cereal	¾cup	42
Pork sausage	1 oz	31
Egg yolk	1	25

Source: USDA2002.

Vitamin D is also available in dietary supplements. While few supplements contain vitamin D alone, many calcium supplements also contain vitamin D. Multivitamin supplements contain up to 400 IU of vitamin D. The amount of vitamin D in a single dose of many calcium and multivitamin supplements may not be sufficient to meet the recommended levels, especially for people over age 70 who need 600 IU per day.

To make sure that the recommended amount of vitamin D is consumed as shown in Table 7-1, check the nutrition label on the supplement for the amount of vitamin D per dose, and, if necessary, supplement vitamin D intake through other sources. However, because vitamin D can have negative effects if taken in very high doses, it is also important to avoid consuming more vitamin D than the tolerable upper level of 2,000 IU per day. Larger doses can initially be given to patients who are deficient as a means of replenishing the stores of vitamin D in the body.

Other Nutrients Important to Bone

As shown in Table 7-1, the Institute of Medicine recently provided recommended intakes for other bone-related nutrients, including phosphorus and magnesium (IOM 1997). Most Americans consume adequate quantities of phosphorus through their regular intake of meats, cereals, milk, and processed foods. While some beverages such as soft drinks also contain phosphorus, they are not a preferred source of phosphorus because they may displace calcium-rich beverages like milk (Whiting et al. 2001).

Magnesium intakes may be suboptimal in those who do not eat enough green leafy vegetables, whole grains, nuts, and dairy products. Fortunately, most diets contain adequate levels of other bone-related micronutrients, such as vitamins K and C, copper, manganese, zinc, and iron, to promote bone health.

Some dietary components may potentially have negative effects on bone health, especially if calcium intakes are not adequate. For example, high levels of sodium or caffeine intake can increase calcium excretion in the urine. The effects of these factors can be overcome by increasing the amount of calcium in the diet (Fitzpatrick and Heaney 2003). Studies have linked excessive amounts of phosphorus to altered calcium metabolism, but it appears that the typical level of phosphorus consumed by most individuals in the United States should not negatively affect bone health (IOM 1997). Excessive amounts of preformed vitamin A (e.g., retinol) can also have negative effects on bone, so individuals should not consume more than the recommended dietary allowance for this vitamin (IOM 2000). The vitamin A precursor (beta carotene) found in many fruits and vegetables does not have negative effects on bone, however.

Table 7-5 provides additional information on other nutrients that affect bone, their recommended dietary allowances, and common dietary sources of these nutrients.

Table 7-5 Other Nutrients and Bone Health at a Glance

Other Nutrients Affecting Bone	What Is the Effect on Bone?	How Much Is Needed?*	What Are the Dietary Sources?	Special Considerations
Potentially Benefical Effects on Bone
Boron	May enhance calcium absorption and estrogen metabolism.	Not applicable.	Raw avocado, nuts, peanut butter, bottled prune juice.
Copper	Copper helps certain enzymes and local regulators function properly so that we can form the optimal bone matrix or structure for bone strength.	RDA is 900 μg for men and women over age 30. Daily intakes over 10,000 μg are not recommended.	Organ meats, seafood, nuts, seeds, wheat bran, cereals, whole grain products, cocoa products.	Calcium supplementation may result in lower levels of copper.
Fluoride	Fluoride stimulates the formation of new bone. Necessary for skeletal and dental development.	RDA is 4 mg for men over age 30 and 3 mg for women over age 30. Daily intakes over 10 mg are not recommended.	Fluoridated water, teas, marine fish, fluoridated dental products.
Iron	Iron helps certain enzymes and local regulators function properly so that we can form the optimal bone matrix or structure for bone strength.	RDA is 8 mg for men over the age of 19. The RDA for women is 18 mg between the ages of 19 and 50 and 8 mg over age 50. Daily intakes over 45 mg are not recommended.	Non-heme sources include fruits, vegetables and fortified bread and grain products such as cereal. Heme sources include meat and poultry.
Isoflavones	Isoflavones have been shown to have a protective effect on bone in animal studies. Evidence in humans, however, is conflicting.	Not applicable.	Primarily found in soybeans and soy products, chickpeas and other legumes.	Ipriflavone, a synthetic isoflavone, has been linked to a reduction in lympocytes, a type of white blood cell that fights infection.
Magnesium	60% of the magnesium in our bodies is found in our bones in combination with calcium and phosphorus. Magnesium appears to enhance our bone quality. Studies suggest that it may improve bone mineral density, and not getting enough may interfere with our ability to process calcium.	RDA is 420 mg for men over 30 and 320 mg for women over 30. Daily intakes over 350 mg are not recommended	Good sources include green leafy vegetables such as spinach, potatoes, nuts, seeds, whole grains including bran, wheat, oats, and chocolate. Smaller amounts are found in many foods including bananas, broccoli, raisins and shrimp. Also found in magnesium-containing laxatives and antacids.	Magnesium deficiency is rare in US adults. Magnesium supplements are not recommended for most people.
Manganese	Manganese helps certain enzymes and local regulators function properly so that we can form the optimal bone matrix or structure for bone strength.	RDA is 2.3 mg for men over age 30 and 1.8 mg for women over age 30. Daily intakes over 11 mg are not recommended.	Nuts, legumes, tea, whole grains and drinking water.	Manganese supplements may not be a good choice for everyone, including people already consuming high levels of manganese from diets high in plant foods and people with liver disease who are especially susceptible to the adverse effects of excess manganese intake.
Phosphorus	Phosphorus is a component of every cell in our bodies and supports building bone and other tissue during growth. About 85% of the phosphorus in our bodies is found in our bones. In fact, phosphate, a form of phosphorus, makes up more than half of our bone mineral mass.	RDA is 700 mg for men and women over age 30. Daily intakes over 4,000 mg for adults up to age 70 and over 3,000 mg after age 70 are not recommended.	Milk, yogurt, ice cream, cheese, peas, meat, eggs, some cereals, breads, cola soft drinks and many processed foods.
Potassium		There is no RDA established for potassium. Scientists recommend a daily intake between 1,600 mg and 3,500 mg.	Milk, yogurt, chicken, turkey, fish, many fruits such as bananas, raisins and cantaloupe, and many vegetables such as celery, carrots, potatoes and tomatoes.
Protein	Proteins are our bodies’ building blocks. We use protein to build tissue during growth and to repair and replace tissue throughout life. We also need protein to help heal fractures and to make sure our immune system is functioning properly.	RDA is 56 g for adult men and 46 g for adult women. Nutritionists recommend that 10% to 35% of our calories come from protein. (The rest come primarily from carbohydrates and fats.)	Complete protein comes from animal sources including meat, poultry, fish, eggs, milk, cheese, yogurt. Incomplete protein comes from plant sources including legumes, grains, nuts, seeds and vegetables.	Getting enough protein is particularly important for elderly people. Studies show that elderly people who have not been getting enough protein and who break their hip are more likely to suffer poor medical outcomes.
Vitamin C	Vitamin C helps certain enzymes and local regulators function properly so that we can form the optimal bone matrix or structure for bone strength.	RDA is 90 mg for men over age 30 and 75 mg for women over age 30. Daily intakes over 2,000 mg are not recommended.	Citrus fruits, tomatoes and tomato juice, potatoes, Brussels sprouts, cauliflower, broccoli, strawberries, cabbage and spinach.	People who smoke need 35 mg more vitamin C than the RDA. People who are regularly exposed to second-hand smoke also may need extra vitamin C.
Vitamin K	Vitamin K helps certain enzymes and local regulators function properly so that we can form the optimal bone matrix or structure for bone strength.	RDA is 120 units for men over age 30 and 90 units for women over age 30. No maximum safe intake has been established for vitamin K.	Green vegetables including collards, spinach, salad greens and broccoli, Brussels sprouts, cabbage, plant oils and margarine.	Patients on anticoagulant medication should monitor their vitamin K intake.
Zinc	Zinc helps certain enzymes and local regulators function properly which in turn helps our bodies form the optimal bone matrix or structure for bone strength.	RDA is 11 mg for boys and men over age19 and 8 mg for girls and women over age 19. Daily intakes over 40 mg are not recommended.	Red meat, poultry, fortified breakfast cereal, some seafood, whole grains, dry beans and nuts.	Nutritionists recommend that vegetarians double the RDA for themselves, because zinc is harder to absorb on a vegetarian diet. Calcium supplementation may reduce the absorption of zinc.
Caffeine	Studies suggest that caffeine may interfere with calcium absorption. However, this effect can be neutralized in the presence of adequate dietary calcium.	Not applicable	Coffee, tea, some soft drinks, some over the counter medications.
Fiber	Fiber has a minor negative impact on calcium absorption.	Men ages 31 to 50 need 38 grams per day and after 50 need 30 grams per day. Women ages 31–50 need 25 gm per day and after 50 need 21 gm per day.	Includes dietary fiber naturally present in grains (oats, wheat or unmilled rice) and functional fiber from plants and animals shown to be of benefit to health.
Oxalates	When oxalates and calcium are found in the same food, oxalates combine with the calcium, preventing us from absorbing the calcium.	Not applicable	Spinach. Other oxalate-rich foods include rhubarb and sweet potatoes, but since these foods do not contain calcium, the oxalates have no effect on calcium absorption.	Oxalates do not interfere with the absorption of calcium in other foods eaten with the oxalate-containing foods.
Phosphorus	Phosphorus is necessary for healthy bones (see above), but some people are concerned that there may be too much in our diet, especially since phosphorus is a component of cola beverages and many processed foods. Some studies suggest that excess amounts of phosphorus may interfere with calcium absorption. The good news is that we can offset the loss by getting adequate amounts of calcium in our diet.	RDA is 700 mg for men and women over age 30. Daily intakes over 4,000 mg for adults up to age 70 and over 3,000 mg after age 70 are not recommended.	Milk, yogurt, ice cream, cheese, peas, meat, eggs, some cereals, breads, cola soft drinks and many processed foods.	Possible negative effects of soft drinks on bone may be due primarily to the replacement of calcium-rich milk with soft drinks, especially by children and teenagers at a time when they need extra calcium to optimize their peak bone mass.
Protein	Protein is essential for good health (see above). However, when we get too much protein, our bodies convert the extra protein into calories for energy, producing a chemical called sulfate in the process. Sulfate causes us to lose some calcium, but these are relatively small losses that we can offset by getting adequate amounts of calcium in our diet.	RDA is 56 g for adult men and 46 g for adult women. It is recommended that 10% to 35% of calories come from protein. (The rest come primarily from carbohydrates and fats.)	Complete protein comes from animal sources including meat, poultry, fish, eggs, milk, cheese, yogurt. Incomplete protein comes from plant sources including legumes, grains, nuts, seeds and vegetables.
Sodium	Sodium affects the balance of calcium in our bodies by increasing the amount we excrete in urine and perspiration. The loss of calcium can be significant, but we can replace the lost calcium by making sure we get adequate amounts of calcium in our diet.	The NIH recommends restricting daily sodium intake to less than 2,400 milligrams (equal to about 1 teaspoon of table salt).	Sodium combined with chloride is common table salt. Many processed foods are high in salt.
Vitamin A	Vitamin A plays an important role in bone growth but excessive amounts of the retinal form of vitamin A may increase the breakdown of our bones and interfere with vitamin D, which we need to help us absorb calcium. The beta carotene form of vitamin A does not appear to cause these problems.	RDAs are 3000 IU for men and 2330 IU for women. Daily intakes over 10,000 IU of the retinol form of vitamin A are not recommended.	Retinol sources include animal-source foods such as liver, egg yolks, cheese, milk. Dietary supplements and some acne preparations also contain retinol. Beta carotene sources include plant-source foods, such as dark orange and green vegetables including carrots, sweet potatoes, and spinach as well as cantaloupe and kale.

Physical Activity

The foundation of a good physical activity regimen involves at least 30 minutes (adults) or 60 minutes (children) of moderate physical activity every day. This regimen can and should involve a variety of activities. Some can be routine activities like walking or gardening. Others may occur more infrequently and differ from day to day and week to week, such as dancing, aerobic classes, biking, swimming, tennis, golf, or hiking. However, it is clear from the evidence presented in Chapter 6 that physical activity to specifically benefit bone health should involve loading (stressing) the skeleton. As a result, weight-bearing activities such as walking should be included in an optimal physical activity regimen to benefit the musculoskeletal system. Moreover, the evidence suggests that the most beneficial physical activity regimens for bone health include strength-training or resistance-training activities. These activities place levels of loading on bone that are beyond those seen in everyday activities; examples include jumping for the lower limbs and weight lifting or resistance training for the lower and upper skeleton. Finally, while a focus on activities that build or maintain bone strength is appropriate and necessary, many older individuals will remain at high risk of fracture. For these individuals, balance training can provide the added benefit of helping to prevent potentially injurious falls.

As noted in Chapter 6, the evidence does not lead to a specific set of exercises or practices but rather a set of principles that can be applied and varied according to the age and current physical condition of an individual. Many of these principles have been reviewed by expert panels of the American College of Sports Medicine (ACSM) (Kraemer et al. 2002, ACSM 1998a, ACSM 1998b) and they lead to the following suggestions for the frequency, intensity, length, and type of physical activity regimens to benefit bone health for individuals of all ages:

• Since continued physical activity provides a positive stimulus for bone, muscle, and other aspects of health, a lifelong commitment to physical activity and exercise is critical.
• Ending a physical activity regimen will result in bone mass returning to the level that existed before the activity began. Since repetitive programs of physical activity may be discontinued due to lack of motivation or interest, variety and creativity are important if physical activity is to be continued over the long term.
• Physical activity will only affect bone at the skeletal sites that are stressed (or loaded) by the activity. In other words, physical activity programs do not necessarily benefit the whole skeleton, although any type of activity provides more benefit to bone than does no activity at all.
• For bone gain to occur, the stimulus must be greater than that which the bone usually experiences. Static loads applied continuously (such as standing) do not promote increased bone mass.
• Complete lack of activity, such as periods of immobility, causes bone loss. When it is not possible to avoid immobility (e.g., bed rest during sickness), even brief daily weight-bearing movements can help to reduce bone loss.
• General physical activity every day and some weight-bearing, strength-building, and balance-enhancing activities 2 or more times a week are generally effective for promoting bone health for most persons.
• Any activity that imparts impact (such as jumping or skipping) may increase bone mass more than will low- and moderate-intensity, endurance-type activities, such as brisk walking. However, endurance activities may still play an important role in skeletal health by increasing muscle mass and strength, balance, and coordination, and they may also help prevent falls in the elderly. Endurance activity is also very important for other aspects of health, such as helping to prevent obesity, diabetes, or cardiovascular disease.
• Load-bearing physical activities such as jumping need not be engaged in for long periods of time to provide benefits to skeletal health. In fact, 5–10 minutes daily may suffice. Most adults should begin with weight-bearing exercise and gradually add some skipping and jumping activity. Longer periods (30–45 minutes) may be needed for weight training or walking/jogging. Those who have been inactive should work up to this amount of time gradually using a progressive program, e.g., start with shorter times and easier activities (light weights or walking) and then increase time or intensity slowly (by no more than 10 percent each week) in order to avoid injury.
• Physical activities that include a variety of loading patterns (such as strength training or aerobic classes) may promote increased bone mass more than do activities that involve normal or regular loading patterns (such as running).

These fundamental principles can be used to develop age-specific regimens, as outlined in the sections that follow.

Physical Activity for Children and Adolescents

For children over age 8 and adolescents, a bone-healthy program of physical activity could include the following:

• At least 60 minutes of moderate intensity, continuous activity on most days, preferably daily. This level of activity can help achieve a healthy body weight and lower the risk of other diseases such as cardiovascular disease and diabetes (USDHHS 1996, USDA 2000, USDHHS 2000, IOM 2002).
• Inclusion of weight-bearing and short, intense impact activities such as basketball, gymnastics, and jumping as part of this regular activity program.
• Performance of weight-bearing activities that increase muscle strength, such as running, hopping, or skipping. The best activities work all muscle groups. Examples include gymnastics, basketball, volleyball, bicycling, and soccer. Swimming, while highly beneficial to many aspects of health, is not a weight-bearing activity and thus does not contribute to increased bone mass.

Table 7-6Weight-Bearing Exercise for Kids and Teens

Exercise helps build bone and weight-bearing exercise is particularly helpful in this task. Weight-bearing exercise includes any activity in which your feet and legs carry your own weight. Here are some examples of weight-bearing exercise that can help you build strong bones:

• Walking
• Running
• Jumping
• Jumping rope
• Dancing
• Climbing stairs
• Jogging
• Aerobic dancing
• Hiking
• Inline skating/ice skating
• Racquet sports, such as tennis or racquetball
• Team sports such as soccer, basketball, field hockey, volleyball, and softball or baseball

Source: NICHD 2004.

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More information: Dorothea Dumuid et al. The “Goldilocks Day” for Children’s Skeletal Health: Compositional Data Analysis of 24‐Hour Activity Behaviors, Journal of Bone and Mineral Research (2020). DOI: 10.1002/jbmr.4143