Exercise may improve a woman’s chances of becoming pregnant, a University of Queensland study has found.
Dr. Gabriela Mena, from UQ’s School of Human Movement and Nutrition Sciences, analyzed research on reproductive health and exercise from the last two decades.
“When physical activity was compared with standard fertility treatments, such as IVF or ovulation induction, there was no difference in pregnancy rates and live births between women exercising and those undertaking fertility treatments,” Dr. Mena said.
“This suggests that physical activity may be as effective as commonly-used fertility treatments, and could be an affordable and feasible alternative or complementary therapy to these very expensive treatments.
“We also found higher pregnancy and live births rates for women who were physically active than women not undertaking exercise or undergoing fertility treatments.”
Dr. Mena said no particular type of exercise was identified as better than any other.
“There were different types of physical activity in the studies reviewed, such as aerobic training alone or in conjunction with strength training, but even moderate increases in physical activity – such as increasing the step counts – seemed to improve reproductive health outcomes,” she said.
“We believe that a combination of aerobic and resistance training is good for improving reproductive health, but it is difficult to recommend a particular type of exercise at this stage.
“There is still a need for more studies that focus on physical activity in women who have problems with fertility.
“Studies with different types of exercise, intensity and duration are required in order to find the optimal ‘dose’ or prescription of physical activity.
“We also need more evidence about women experiencing problems with fertility on whether they will exercise – can they do it? Will they do it?
And if so, what would they like to do? – my future research aims to answer these questions.”
The study is published in Human Reproduction Update.
An estimated 15% of couples in the United States (U.S.) are affected by infertility, defined as the failure to achieve pregnancy after 12 months of unprotected sexual intercourse (3).
Although infertility is often associated with women, male physiological factors have been shown to be responsible for ~25% of cases, underscoring the need to consider both partners (4).
The incidence of infertility has remained high despite increased use of assisted reproductive technologies (ART) in recent years (5).
As such, research has aimed to identify modifiable risk factors for infertility; to date, nutritional factors have been the subject of much of this investigation.
Evidence suggests that nutrition can play an important role in altering fertility-related outcomes in both men and women (5).
The purpose of this article is to summarize the literature on the nutritional factors related to infertility and to consider the public health implications of this body of research within the landscape of the U.S (Figure (Figure11).
Overall dietary patterns
There is strong evidence that healthy preconception dietary patterns among both men and women of reproductive age have a beneficial effect on fertility.
A dietary pattern consistent with the recommendations put forth by the U.S. Dietary Guidelines for Americans, which recommends a high consumption of whole grains, monounsaturated or polyunsaturated oils, vegetables, fruits, and fish (6), has been associated with improved fertility in women and higher semen quality in men (5).
In the Nurses’ Health Study (NHS) II, a large prospective cohort, women who had the highest intake of a “fertility diet” comprised of plant protein from vegetable sources, full-fat dairy foods, iron, and monounsaturated fats, during the preconception period, were found to have a 66% (95% CI, 52, 77%) lower risk of infertility related to ovulatory disorders and a 27% (95% CI, 5, 43%) lower risk of infertility due to other causes compared to women with the lowest intake of this diet pattern, controlling for age, body mass index (BMI), alcohol intake, coffee intake, smoking, and oral contraceptive use (7).
Population attributable risk calculations based on this sample suggest that not following the “fertility diet” was the attributable factor in 46% of cases of infertility, which was higher than all other independent risk factors (e.g., BMI, physical activity) (7).
In another study of college-educated women in Spain, those in the highest quartile of adherence to a Mediterranean-style diet, which similarly included high intake of vegetables, fish, and polyunsaturated oils, had 44% (95% CI, 35, 95%) lower odds of seeking medical help for difficulty getting pregnant compared to women in the lowest quartile (8).
The Mediterranean diet yielded similar benefits on achieving clinical pregnancy and live birth among non-obese women in Greece, but only for those below the age of 35 (9).
Furthermore, data indicate that a healthy diet, consisting of the aforementioned food groups, improves measures of semen quality, including morphology, motility, and concentration (4).
Specific foods and nutrients
Data on the associations of specific nutrients and foods with fertility may yield important insight into the possible mechanisms linking diet and reproductive health.
In addition to being linked to neural tube defects in infants, low levels of folate are associated with a lower frequency of sporadic anovulation (10).
In a randomized controlled trial of subfertile women who took a multivitamin containing 400 μg of folic acid for 3 months, 26% had a pregnancy compared to 10% of women in the placebo group (11).
However, the dose-response benefit of folate appears to extend beyond the current recommended dose for reproductive-aged women (400 μg).
Gaskins et al. (10) found that higher levels of pre-pregnancy folate supplementation were associated with a lower risk of spontaneous abortion, but only when comparing those who consumed greater than 730 μg per day of supplemental folate with those who did not consume any folate from supplements.
Preliminary data suggest that red meat may have an adverse effect on fertility. Results from an infertility cohort study showed that consumption of red meat was negatively associated (OR: 0.81; 95% CI, 0.65, 0.99) with likelihood of blastocyst formation during embryo development (12).
Notably, iron intake may be reduced if red meat intake is restricted; yet it has been shown that consuming iron supplements and non-heme iron from other sources may decrease the risk of ovulatory infertility (13).
Saturated fat content, which can be particularly high in red meat, has independently been linked to lower semen concentration in males (14).
Polyunsaturated fats, conversely, have been shown to yield reproductive benefits in both men and women.
A cross-sectional study of men showed that higher intake of omega-3 fatty acids was associated with significantly more favorable sperm morphology (14).
Women who consumed higher levels of omega-6, linoleic acid, and omega-3 had a higher incidence of pregnancy than those with lower intake of these nutrients (15).
Current research examining the effect of dairy on fertility is limited in scope (5).
One study found few and inconsistent associations between preconception dairy intake and fertility in two cohorts of reproductive-aged women (16).
In the NHS II, however, while no relationship was found between total intake of dairy products and risk of infertility, full-fat dairy products were associated with a lower risk of ovulatory infertility while low-fat dairy products (including skim, 1%, and 2% milk, yogurt, or cottage cheese) were associated with a higher risk (17).
Studies have similarly yielded inconclusive evidence on the effect of alcohol and caffeine intake on fertility.
Chavarro et al. (18) found that neither alcohol nor caffeine intake appeared to impair ovulation to the point of decreasing fertility in NHS.
While men with caffeine intake greater than 272 mg/day and alcohol intake over 22 g/day have been linked to lower adjusted live birth rates after use of ART, intake of these substances has not been shown to affect semen quality (19).
In another prospective cohort study of 3,628 women planning to become pregnant, women who reported consuming 3 or more servings of soda per day had a 52% lower (95% CI, 0.21, 1.13) rate of pregnancy compared to women who did not report any soda consumption, while there was no association found between coffee consumption and fertility (20).
These results may be indicative of the adverse effects of sugar intake on fertility among women, although further studies on this topic are needed. Existing data suggest that high consumption of sugar is associated with lower semen quality and increased infertility among men (21).
Body mass index
Current research indicates a roughly “J”-shaped relationship between BMI and fertility, such that the risk of infertility is highest among those at the lowest and highest ends of the BMI distribution (7).
In the NHS II, compared to women classified as having recommended weight (BMI 20–25 kg/m2), a higher risk of ovulatory disorder infertility was observed for women classified as underweight (BMI < 20 kg/m2; RR: 1.38; 95% CI, 1.03, 1.85) and for women with obesity (BMI ≥ 30 kg/m2; RR: 2.35; 95% CI, 1.78, 3.11), after controlling for diet, age, smoking, and oral contraceptive use (7).
Additionally, a review of the literature related to male obesity and fertility concluded that male obesity is associated with increased risk of infertility, potentially through endocrine dysregulation mechanisms (22).
Obesity status has also been linked to ART treatment success. Among a nationally representative sample of U.S. women using ART, a BMI between 30 and 35 kg/m2 was associated with significantly greater odds (OR: 1.14; 95% CI, 1.09, 1.19) of failing to achieve a clinical intrauterine gestation compared to women in a reference group with BMI 18.5-25 kg/m2 (23).
There is limited data on the extent to which BMI modifies the relationship between dietary (and other) factors and infertility. Chavarro et al. (7) found that the relationship between an ideal dietary pattern and risk of infertility was not modified by BMI; although the absolute risk of ovulatory disorder infertility was higher in those with a BMI over 25 kg/m2 compared to those with a recommended BMI; the extent to which dietary improvements attenuated that risk was similar in both groups. Furthermore, physical activity levels also reduced the risk of ovulatory disorder infertility similarly across BMI categories (7).
A recent systematic review explored the impact of weight loss interventions among participants with overweight or obesity status on fertility-related outcomes (24).
Among women, a pooled analysis of randomized studies found that participants randomized to active diet and exercise interventions were more likely (RR: 1.59; 95% CI, 1.01, 2.50) to become pregnant compared to control participants.
Public health implications of the diet-fertility connection
Integration of nutrition counseling into fertility treatment
Given the rigorous evidence presented above that suggests that various aspects of nutrition contribute to a reduced risk of fertility problems in the general reproductive-aged population and may also be an effective treatment for men and women already experiencing infertility, nutrition, and/or obesity counseling is likely to be central in fertility treatment.
Obesity assessment is customary during the treatment process; 43% of U.S.-based infertility clinics included in a survey had a BMI cutoff for performing ART procedures, while 83% of the directors of clinics surveyed believed that a standard cutoff should exist (25).
When asked about the weight loss method that they recommended to patients with an elevated BMI, 95% of respondents reported that they counseled their patients on proper diet and exercise, and 90% reported referring their patients to a nutritionist (25).
This course of action is promising given the effectiveness of weight loss interventions on fertility outcomes (24).
However, as noted above, evidence suggests that following a healthy diet provides a similar magnitude of benefit on fertility regardless of BMI status (7). T
hus, it may be prudent to consider expanding weight-loss or nutritional advice to all individuals accessing infertility treatment, while continuing to prioritize those who are below or above certain BMI cutoffs.
One way to support this would be to include nutritional counseling in national clinical guidelines for fertility.
For example, the National Institute for Health and Care Excellence in the United Kingdom included in their 2013 fertility treatment guidelines that providers should inform patients experiencing difficulty becoming pregnant that either partner having a BMI > 30 kg/m2 may have a reduced chance of conception, and that losing weight might improve the chances of becoming pregnant (26).
Nonetheless, fertility-promoting diets are not specifically mentioned in these clinical practice guidelines.
Nutrition and the psychological burden of infertility
Women who experience issues with fertility are at an increased risk of depression relative to women not experiencing such problems (2).
Moreover, women with pre-existing depression may be more likely to experience infertility due to physiological changes in hormone production and ovulation (27).
A recent meta-analysis reported higher achievement of pregnancies or live births among women with lower pre-pregnancy depression or anxiety (28).
Moreover, among men, exposure to occupational stressors was negatively associated with semen quality (29).
As such, it is critical to understand how to manage depression and other psychosocial factors in women and men who are contemplating or having difficulty becoming pregnant. Beyond the effect of a healthy diet on fertility-related outcomes, certain dietary patterns have been shown to protect against depression.
For example, participants randomized to a Mediterranean diet had a lower risk of depression compared to control participants who were assigned to a low-fat diet, especially among those with preexisting type 2 diabetes (30).
Furthermore, the relationship between low folate status, a risk factor for subfertility, and depression has been well-characterized in the literature (31).
Therefore, promoting healthy dietary patterns and higher folate intake among individuals experiencing infertility may improve their chances of achieving a pregnancy and concomitantly temper the psychological burden associated with their experience.
However, current guidelines for psychosocial counseling in infertility treatment do not include nutritional advice as a factor that clinicians should consider (32).
Consideration of fertility when developing nutritional guidelines
While several foods and nutrients that may protect against infertility are consistent with current federal nutrition guidelines – such as the USDA Dietary Guidelines for Americans (6)—the connection between diet and fertility is not mentioned.
This omission may limit recommendations of foods and nutrients that have strong evidence for improved fertility at the population level. For example, women of reproductive age are recommended to consume 400 μg of folic acid per day, but evidence suggests that higher consumption pre-pregnancy may lower the risk of some infertility outcomes (10).
Furthermore, while fish high in omega-3 fatty acid content are generally recommended as part of a healthy diet, there is potential for environmental contamination from mercury and other toxins in some specific type of fish.
Although studies have reported mostly null associations between mercury intake and fertility or reproductive outcomes (33–36), specific recommendations for fish intake are made for pregnant women or women of childbearing age (37).
Nonetheless, omega-3 fatty acid intake should still be recommended to these groups as part of a healthy fertility diet (38). Recognizing the types and quantities of foods that contribute to reproductive health may improve national nutrition guidelines.
Nutrition and sociodemographic disparities in infertility
In the U.S., women with lower income or lower educational attainment experience a higher prevalence of infertility outcomes compared to those with higher income or educational attainment, while Hispanic and non-Hispanic Black women have a higher prevalence of infertility compared to non-Hispanic white women (1, 39).
The disparity in fertility rates may partially be explained by nutritional intake, as recent data from a large cohort (n = 7,511) of nulliparous women showed that in the months prior to conception, women with lower educational attainment or who were Hispanic or non-Hispanic Black, had a poorer general diet than women with higher educational attainment or who were non-Hispanic White (40).
Disparities have also been reported in receipt of preventive services for optimal diet and health for conception among U.S. women and men of reproductive age (41).
These results reflect the current state in the general U.S. population, as groups who are racial/ethnic minorities or have lower education tend to have poorer diet quality as well as a higher prevalence of obesity, which is another risk factor for infertility (42).
More information: Gabriela P Mena et al. The effect of physical activity on reproductive health outcomes in young women: a systematic review and meta-analysis, Human Reproduction Update (2019). DOI: 10.1093/humupd/dmz013
Provided by University of Queensland