A guiding maxim among endocrinologists is that pediatric medicine is altogether different from adult medicine. However, it’s also true that pre-adult health has direct consequences during adulthood. Three new, very different studies on children published recently in The Endocrine Society’s Journal of Clinical Endocrinology & Metabolism (JCEM) demonstrate how critical childhood health is, because early insults can cause lifelong impairment. Some pediatric nutritional deficiencies, toxic exposures, and even lifestyle habits are the culprits of some of the most serious adult conditions. As childhood morbidity can cause adult mortality, these problems are important public health priorities.
Optimal iodine nutrition in pregnant women is essential for full fetal development. Congenital hypothyroidism due to maternal iodine defi ciency is the most common preventable cause of intellectual disability worldwide. Some estimates put as many as 2 billion people (~40% of the global population, particularly in developing countries and mountainous and inland areas remote from iodinecontaining marine life) at risk for iodine deficiency. A new study published in the May issue of JCEM preliminarily shows that even mild iodine deficiency (defined as a maternal urinary concentration less than 150 μg/L) during pregnancy might be associated with cognitive impairment. Initiatives to reduce salt intake, vegan diets, and lack of information (particularly in low socioeconomic status [SES] populations) about iodine as an essential nutrient are contributing to mild iodine deficiency also in the developed world.
Kristen L. Hynes, PhD, of the Menzies Research Institute at the University of Tasmania in Australia and her team of scientists found not only that even mild deficiency during pregnancy can harm the baby’s neurological development but also that children experience the adverse effects of insufficient iodine for years after birth, as evidenced by poorer literacy test scores. Unfortunately, providing iodine after birth did not mitigate the gestational insufficiency, as scientists formerly thought, heightening this public health problem. “Although the participants’ diet was fortified with iodine during childhood, later supplementation was not enough to reverse the impact of the deficiency during the mother’s pregnancy,” says Hynes.
Her team reviewed national and state standardized test scores of the Gestational Iodine Cohort, 228 Tasmanian children born between 1999 and 2001, when the Tasmanian population as a whole experienced iodine deficiency until bread manufacturers began fortifying bread with iodized salt in late 2001. At age nine years, the study participants born to mothers with gestational iodine deficiency had 5.7% lower overall literacy skills, 7.6% lower grammar skills, and 10.0% lower spelling skills than those who did not experience gestational iodine deficiency. Because the deficit in spelling was so pronounced, whereas no deficit was found in math performance, Hynes and colleagues suggest that auditory pathway development and, consequently, auditory working memory are most affected by inadequate iodine.
“Fortunately, iodine deficiency during pregnancy and the resulting neurological impact is preventable,” Hynes says. “Pregnant women should follow public health guidelines and take daily dietary supplements containing iodine.” In the U.S., the Institute of Medicine puts the current recommended dietary allowance for iodine at 220 μg and 290 μg daily for pregnant and breastfeeding women, respectively (a teaspoon of iodized salt contains ~400 μg iodine). The World Health Organization recommendation is comparable at 250 μg daily for both pregnant and lactating women. Furthermore, says Hynes, “public health supplementation programs also can play a key role in monitoring how much iodine the population is receiving and acting to ensure at-risk groups receive enough iodine in the diet.” Accordingly, the American Thyroid Association recommends that all pregnant and breastfeeding women take a prenatal multivitamin daily containing 150 μg iodine. Most iodine-containing multivitamins have at least 150 μg of iodine, but it’s important to remind patients that about half of the types of U.S. multivitamins do not contain iodine and to choose carefully.
Where There’s Smoke
Just as a lack of a substance can impair childhood health, the opposite is also true when too much of a substance — even indirect exposure — can create adverse effects that persist throughout the lifespan. A large population-based longitudinal study also published in the May JCEM found that long-term secondhand smoke is one such substance, interfering with high-density lipoprotein cholesterol (HDL-C) levels. Insofar as HDL-C clears cholesterol from the blood for breakdown by the liver, thereby, preventing the atherosclerosis that results from cholesterol accumulation, it is an important endogenous heart disease combatant.
Chi Le-Ha, MD, of the University of Western Australia in Perth, led a team of researchers to study smoking practices in the homes of 816 adolescents born between 1989 and 1992, from the time their mothers were pregnant to the time the participants were 17 years old, when the researchers measured their HDL-C levels via blood sample. Of the cohort, 48% were exposed to secondhand smoke in utero and/or in the home. Girls exposed to passive smoking showed significantly lower levels of circulating HDL-C compared to unexposed girls, a relationship not replicated in boys.
Thus, girls may be more vulnerable to the detrimental effect of secondhand smoke exposure.
He-La says these findings are very important in the context of preventing heart disease, the leading cause of death in women in the Western world. “Both low levels of HDL-cholesterol and cigarette smoking — active and passive — are major risk factors of cardiovascular disease in adults. We have learned that atherosclerosis begins in childhood, that the lipids are expressed in childhood, and that they track from childhood to adulthood. Hence, starting treatment of risk factors early in life is essential to prevention of heart disease later.”
Although smoking in public has largely been eradicated, smokers may consider the home a safe smoking haven. Public health eff orts to educate smokers on the lifelong adverse eff ects of passive smoke on their children — especially girls — are paramount here, adds Le-Ha. Infant exposure to secondhand smoke is also associated with low birth weight, sudden infant death syndrome, and respiratory distress syndrome. The earlier the exposure, the more pronounced the negative impact may be.
Treating lifestyle risk factors early is also important in the pediatric population. We know that children require regular physical activity for optimal physical health, but those who aren’t getting enough may be at risk for mental impairment in addition to physical. Though many studies report a link between mental and physical well-being, the connection is not well understood. “Findings in adults have suggested that the adaptation of the hypothalamic-pituitary-adrenocortical axis (HPAA), one of the main stress response systems in humans, caused by physical exercise might generalize to other stressors as well, such as psychosocial ones,” says Silja Martikainen, MA, of the University of Helsinki, Finland, the lead author of a recent paper on the effects of exercise on stress in children that was published in the April issue of JCEM.
In their cross-sectional study, the researchers administered the Trier Social Stress Test for Children to 258 Finnish eight-year-olds and then measured their salivary cortisol levels. They report little or no increases in stress hormone levels in those with high levels of activity measured by wrist accelerometers, compared to those with a low level of physical activity, even though diurnal salivary cortisol profiles were similar in both groups.
Thus, the highly active children had lower HPAA reactivity to stress, suggesting that exercise promotes mental health by regulating the stress hormone response to psychosocial stressors. Alternatively, the findings could suggest that a sedentary lifestyle itself causes susceptibility to psychosocial stress, as a result of higher HPAA reactivity. “As these finding are from a cross-sectional study, the causality of the effect cannot be identified,” says Martikainen. “These results call for prospective controlled studies, such as intervention studies, to further investigate whether physically active lifestyle or physical exercise could alleviate hormonal responses to psychosocial stress,” she adds.
Given that sustained cortisol exposure disrupts many body systems, leading to everything from heart disease to obesity to depression, the benefits of regulation strategies are clear. Demographics show that low SES kids have the highest inactivity rates. If exercise is the body’s built-in regulatory system, funding to promote exercise programs for kids age two years and older is needed. Th e American Heart Association recommends at least 60 minutes of enjoyable, moderate-intensity physical activities daily that are developmentally appropriate and varied. Inactivity begets inactivity; the earlier interventions can happen, the better.
With recent pediatric studies demonstrating time and again that environmental health insults in childhood have ramifications through adulthood, the impact of such insults cannot be overstated. Public health efforts will be critical in each of these areas (i.e., iodine supplementation, secondhand smoke avoidance, and adequate physical activity) to educate high-risk groups, and physicians are important public health stakeholders to help disseminate that information. Th e pediatric care opportunity window cannot be squandered — the burden of enjoying a healthy adulthood seems to fall largely on health care in childhood because many negative effects are simply irreversible, even when the environmental condition is reversed.
— Horvath is a freelance writer in Baltimore and a regular contributor to Endocrine News.