Adolescents exposed to multiple adversities early in life have lower IQ scores

Preschoolers living in impoverished communities who have access to a nurturing home environment have significantly higher intelligence quotient (IQ) scores in adolescence compared to those raised without nurturing care.

That is the finding of a new international study conducted by University of Maryland School of Medicine (UMSOM) researchers, which examined data from more than 1600 children from Brazil and South Africa who were followed from birth through their teenage years.

Results were published this week in The Lancet Child & Adolescent Health journal.

The researchers analyzed data from long-running studies conducted in Brazil and South Africa to assess whether children exposed to early adversities (such as extreme poverty, low birth weight, or pre-term birth) could reach their full learning potential by experiencing responsive caregiving and opportunities to learn in their home.

They found that prenatal and early life adversities matter throughout life. Adolescents who had been exposed to multiple adversities early in life had lower IQ scores, were more likely to have difficulties adjusting socially and psychologically, and achieved a lower physical height compared to adolescents exposed to fewer adversities.

They also found that being raised in a nurturing environment could significantly counteract the detrimental effect of early adversities on IQ and help children achieve their full intellectual potential.

“We found that adolescents who were raised in nurturing environments had IQ scores that were on average 6 points higher than those who were not. This is a striking difference that has profound implications by increasing the intelligence of entire communities,” said study corresponding author Maureen Black, Ph.D., the John A Scholl and Mary Louise Scholl Endowed Professor of Pediatrics at UMSOM.

“A nurturing environment also led to better growth and fewer psycho-social difficulties in adolescence, but it did not mitigate the effects of early adversities on growth and psycho-social difficulties.”

Globally, more than 250 million children younger than 5 years are at risk of not reaching their developmental potential because of adversities that co-occur early in life and accumulate with age. In the U.S, almost one in five children are raised in poverty and 15 percent do not complete high school, with higher rates for children in Black and Hispanic families. Exposing these children to a nurturing environment, whether at home or in daycare or pre-school settings, can lead to cognitive benefits that last into adolescence and beyond.

“I think our findings could apply to communities here in the U.S. where children are hungry, living in poverty or lacking in access to medical care,” Dr. Black said.

Added study lead author Angela Trude, Ph.D., a post-doctoral fellow in the UMSOM Department of Pediatrics, “Parents want to provide nurturing environments and we need to help them.” She said this includes interacting with young children in a positive way such as reading children’s books from the library, singing songs together, and playing games with numbers and letters.

Children who engage in age-appropriate chores with adult supervision like picking up toys and clearing the table gain skills and feel good about helping.

“Get children involved in friendly activities as much as possible rather than parking them in front of a screen,” Dr. Black said. “Children love to learn and in a nurturing environment they can grow into adolescents and adults with the abilities to care for themselves, their families, and their communities.”

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Adversity experienced during childhood and adolescence can have substantial consequences for developmental processes throughout the life course (1). Childhood adversity refers to a broad array of negative events experienced during the early years of life and into adolescence (2). The consequences of childhood adversity may affect social (3, 4), affective (5, 6), and cognitive development (7–9). Here, we examined the links between childhood adversity and intelligence in a general population sample.

Intelligence is currently defined by a generalized intelligence factor (g) that is composed of subdimensions, such as visuospatial reasoning, language, and working memory (10, 11). A widely accepted model of cognitive functioning distinguishes between fluid and crystallized intelligence as 2 primary components (12). Fluid intelligence reflects reasoning and the ability to solve novel problems; crystallized intelligence reflects knowledge and skills from learned experiences (13) and is considered a valid measure of generalized intelligence (14, 15).

Studies examining the association between childhood adversity and intelligence have identified negative correlations resulting from physical and sexual abuse (16–19) and exposure to violence (20, 21). These types of experiences are characterized as threats of harm to one’s physical integrity (22).

The effects of threat experiences may influence development of many different brain regions through well-characterized stress pathways (23, 24), associated with reductions in hippocampal volume and associated parahippocampal regions (25–28), which may in turn influence learning and memory (29).

There is also evidence that growing up with chronic exposure to neglect (30–33) and poverty (34, 35) may affect cognitive functioning. These deprivation-type experiences are characterized by an absence of expected environmental inputs (e.g., complex language, consistent interactions with caregivers) and an absence of cognitive stimulation (22, 36).

Children raised in environments that may lack cognitive stimulation, including poverty, neglect, and institutional rearing, have consistently shown reduced cognitive ability, which may be mediated by accelerated and extreme synaptic pruning in cortical regions involved in complex cognitive functions in response to an absence of expected environmental inputs (30, 36–39).

Childhood adversity is a multidimensional experience, which can make it challenging to model analytically. Most studies make unverified assumptions about the relationship between multiple childhood adversities and related outcomes. For example, studies often examine the effects of individual (40) or a linear accumulation of adversities (41) or use a latent variable framework (42).

Applications of these approaches have relied on the assumptions that the effect of each adversity can be estimated independently of other adversities (i.e., no interaction between adversities), and that the effect of cumulative exposures is linear. There are 2 additional limitations from studies of adversity and cognition.

Few studies use a standardized measure of intelligence, making comparisons across studies difficult. Furthermore, most studies use data from small samples with potentially limited generalizability.

Although these studies allow for an investigation of specific adversities, using a national sample allows for study of a broader set of exposures in a population-representative context, increasing the likelihood that results will be broadly relevant (43).

We hypothesized that both threat- and deprivation-type adversities would be significantly associated with intelligence but that associations would be largest for adversities reflecting deprivation. To address the above limitations and test this hypothesis, we investigated the relationship between childhood adversity and a standardized measure of intelligence in a population-representative sample of US adolescents. We addressed the limitations in modeling multiple adversities by examining these relationships using targeted maximum likelihood estimation (TMLE). TMLE is a semiparametric estimation method that can be used to minimize bias in the relationship between each adversity and the outcome, including interactions and nonlinearity (44)

RESULTS

Figure 1 presents the mean differences comparing the K-BIT scores if all adolescents had experienced a given adversity with the mean in the absence of that adversity. There were significant differences in K-BIT mean scores among those who reported ever experiencing several types of threat experiences, including physical abuse and domestic violence. Experiencing any threat was associated with a mean score of 1.82 (95% confidence interval: 0.82, 2.83) units lower than no threat experience.

Among deprivation experiences, there were significant mean differences in K-BIT associated with a household income at the poverty line, having parents with less than a high school diploma, and having financial insecurity. Experiencing any deprivation was associated with a mean score of 2.32 (95% confidence interval: 1.21, 3.43) units less than those with no experience of deprivation. Full results are presented in Table 1. There was no evidence of a dose-response relationship with greater cumulative adversities.Figure 1.

Table 1.

Targeted Maximum Likelihood Estimated Mean Scores on the Kaufman Brief Intelligence Test in the Presence Versus Absence of Individual and Cumulative Childhood Adversities Among a Representative Sample of Adolescents (n = 10,073), United States, 2001–2004

Adversity Type	Mean K-BIT Scorea	95% CI	K-BIT Mean Difference	95% CI
Threat adversities
Physical abuse	98.8	97.3, 100.2	–1.97	–3.42, –0.52
No physical abuse	100.8	99.3, 102.2
Domestic violence	99.1	97.3, 100.8	–1.86	–3.60, –0.11
No domestic violence	100.9	99.2, 102.7
Sexual abuse	101.3	98.4, 104.2	1.27	–1.63, 4.18
No sexual abuse	100.1	97.2, 103.0
Violence	101.3	99.3, 103.3	1.09	–0.90, 3.07
No violence	100.2	98.2, 102.2
Witnessing violence	99.9	98.3, 101.4	–1.22	–2.80, 0.36
No witnessing violence	101.1	99.5, 102.7
Emotional abuse	99.5	97.5, 101.5	–1.81	–3.82, 0.20
No emotional abuse	101.3	99.3, 103.3
No. of cumulative threat-experience adversities
1	99.4	98.2, 100.6
2	100.1	98.4, 101.9
≥3	100.3	97.8, 102.8
≥1	100.5	99.5, 101.6	–1.82	–2.83, –0.82
0	102.4	101.4, 103.4
Deprivation adversities
Income-to-poverty ratio < 1.5	98.6	97.7, 99.4	–2.29	–3.12, –1.46
Income-to-poverty ratio ≥ 1.5	100.9	100.0, 101.7
Parental education < HS diploma	97.3	95.5, 99.2	–3.58	–5.40, –1.75
Parental education ≥ HS diploma	100.9	99.1, 102.8
Financial insecurity	99.6	98.1, 101.2	–1.55	–3.11, 0.01
No financial insecurity	101.2	99.6, 102.7
Food insecurity	99.6	98.2, 101.1	–1.41	–2.89, 0.07
No food insecurity	101.0	99.6, 102.5
Neglect	98.0	93.4, 102.7	–4.27	–8.93, 0.39
No neglect	102.3	97.6, 106.9
No. of cumulative deprivation experiences
1	99.9	98.8, 101.0
2	98.4	95.6, 101.1
≥3	98.8	96.0, 101.7
≥1	99.2	98.1, 100.3	–2.32	–3.43, –1.21
0	101.5	100.4, 102.6
No. of cumulative total adversities
1	99.9	98.7, 101.0
2	97.6	92.5, 102.7
≥3	98.6	96.8, 100.4
≥1	99.8	98.7, 100.9	–2.02	–3.09, –0.94
0	101.8	100.7, 102.9

Figure 2 presents the risk of a low versus average K-BIT score if all adolescents had experienced a given adversity compared with the risk in the absence of that adversity. The risk difference of low K-BIT from experiencing any threat was 6 cases per 100 (95% confidence interval: 0.03, 0.10). The specific threat experiences of physical abuse, domestic violence, and emotional abuse were significantly associated with a low K-BIT score. The difference in risk of low K-BIT from experiencing any deprivation experience was 7 cases per 100 (95% confidence interval: 0.03, 0.11). Specifically, having parents with less than a high school diploma and experiencing neglect both significantly increased the risk of a low K-BIT. There was no evidence that the risk differences increased with greater cumulative adversities. Full results are presented in Table 2.Figure 2.

Table 2.

Targeted Maximum Likelihood Estimated Risk Differences for the Risk of Low (<85) Versus Average (≥100) Score on the Kaufman Brief Intelligence Test, Under Individual and Cumulative Adversities Compared With the Risk Absent That Exposure in a Representative Sample of Adolescents (n = 10,073), United States, 2001–2004

Adversity Type	K-BIT Score <85 With Exposurea,b	K-BIT Score <85 Without Exposurea,c	RD	95% CI
Threat adversities
Physical abuse	0.29	0.23	0.06	0.01, 0.10
Domestic violence	0.25	0.20	0.05	0.00, 0.09
Sexual abuse	0.25	0.23	0.01	−0.08, 0.11
Violence	0.22	0.21	0.01	−0.04, 0.06
Witnessing violence	0.28	0.23	0.06	−0.02, 0.13
Emotional abuse	0.31	0.23	0.08	0.01, 0.16
No. of cumulative threat-experience adversities
1	0.28	0.22	0.06	0.02, 0.10
2	0.28	0.23	0.05	−0.01, 0.11
≥3	0.29	0.25	0.04	−0.03, 0.11
≥1	0.24	0.18	0.06	0.03, 0.10
Deprivation adversities
Income-to-poverty ratio < 1.5	0.23	0.22	0.01	−0.02, 0.04
Parental education < HS diploma	0.35	0.22	0.13	0.06, 0.19
Financial insecurity	0.28	0.24	0.04	−0.01, 0.09
Food insecurity	0.27	0.23	0.04	−0.01, 0.09
Neglect	0.34	0.22	0.11	0.02, 0.21
No. of cumulative deprivation-experience adversities
1	0.26	0.23	0.03	−0.01, 0.07
2	0.33	0.22	0.11	0.02, 0.20
≥3	0.35	0.25	0.10	0.03, 0.18
≥1	0.28	0.21	0.07	0.03, 0.11
No. of cumulative total adversities
1	0.26	0.24	0.02	−0.02, 0.07
2	0.35	0.17	0.18	−0.02, 0.38
≥3	0.29	0.22	0.07	0.03, 0.12
≥1	0.26	0.20	0.06	0.03, 0.10

Results from the sensitivity analysis, including parental education as a covariate rather than an adversity can be found in Web Table 3. Overall, K-BIT mean differences were attenuated but remained significant for those experiencing any threat, living near the poverty line, and experiencing any deprivation or any adversity.

reference link: https://academic.oup.com/aje/article/187/7/1456/4812022

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More information: Angela C B Trude et al, Effects of responsive caregiving and learning opportunities during pre-school ages on the association of early adversities and adolescent human capital: an analysis of birth cohorts in two middle-income countries, The Lancet Child & Adolescent Health (2020). DOI: 10.1016/S2352-4642(20)30309-6