Public release date: 13-Sep-2010
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Contact: Hilary Hurd Anyaso
h-anyaso@northwestern.edu
847-491-4887
Northwestern University
Male maturity shaped by early nutrition
Differences between the sexes affected by environment during first six months of life
EVANSTON, Ill. --- It seems the old nature versus nurture debate can't be won. But a new Northwestern University study of men in the Philippines makes a strong case for nurture's role in male to female differences -- suggesting that rapid weight gain in the first six months of life predicts earlier puberty for boys.
Males who experienced rapid growth as babies -- an indication that they were not nutritionally stressed -- also were taller, had more muscle and were stronger, and had higher testosterone levels as young adults. They had sex for the first time at a younger age and were more likely to report having had sex in the past month, resulting in more lifetime sex partners.
The researchers think that testosterone may hold the key to understanding these long-term effects.
"Most people are unaware that male infants in the first six months of life produce testosterone at approximately the same level as an adult male," said Christopher W. Kuzawa, associate professor of anthropology in the Weinberg College of Arts and Sciences and author of the study. "We looked at weight gain during this particular window of early life development, because testosterone is very high at this age and helps shape the differences between males and females."
The study provides more evidence that genes alone do not shape our fate.
"The environment has a very strong hand in how we turn out," Kuzawa said. "And this study extends that idea to the realm of sex differences and male biology."
The study found men, on average, tend to be taller and more muscular than females, and the magnitude of that difference appears to be the result of nutrition within the first six months of an infant male's life, according to the study.
"There is a perennial question about how important heredity is versus the environment as shapers of who we turn out to be," said Kuzawa. "In the last 20 years, a lot has been learned about a process called developmental plasticity -- how the body responds early in life to things like nutrition and stress. Early experiences can have a permanent effect on how the body develops, and this effect can linger into adulthood. There is a lot of evidence that this can influence risk of diseases like heart attack, diabetes and hypertension -- really important diseases."
Kuzawa and his collaborators applied the same framework in this study and found evidence that male characteristics -- such as height, muscle mass and testosterone levels as opposed to disease characteristics -- also relate back to early life developmental plasticity.
"Another way to look at it is that the differences between the sexes are not hard wired, but are responsive to the environment, and in particular to nutrition," Kuzawa said.
Testosterone has long been known to increase muscle mass and puts a person on a higher growth trajectory to be taller. The Northwestern study suggests that the age of puberty also is influenced by events in the first six months of life.
The study, which was funded by the National Science Foundation and the Wenner Gren Foundation, was conducted among a group of 770 Filipino males aged 20 to 22 who have been followed their entire lives. Since 1983 a team of researchers in the United States and the Philippines (including Kuzawa for about the last 10 years) has been working to understand how early life nutrition influences adult health, such as risk for cardiovascular disease and diabetes.
"Rapid Weight Gain After Birth Predicts Life History and Reproductive Strategy in Filipino Males" was published Sept. 13 in the Proceedings of the National Academy of Sciences. The study's co-authors are Thomas W. McDade, associate professor of anthropology, Northwestern University, Linda S. Adair, University of North Carolina at Chapel Hill, and Nanette Lee, University of San Carlos of the Office of Population Studies in Cebu City, Philippines.
First Lady Michelle Obama is reportedly wrestling with at least 100 House Democrats who would rather not pass a re-authorization of the nation's school meals program if it means taking money from food stamp recipients.
The Senate approved the Healthy, Hunger-Free Kids Act, which would increase spending on child nutrition programs by $4.5 billion -- including a 6-cent-per-meal boost to the rate the federal government reimburses school lunch -- but said the only way to fund it without adding to the deficit was to remove $2.2 billion from the food stamp (now known as SNAP) program. Re-authorization of the Child Nutrition Act must now be approved by the House before authorization for the legislation currently in place expires.
The Senate's funding method is a bit like picking the pocket of one panhandler to put it in the hand of another. Yet the mainstream media has hailed these measly 6 cents as the first increase in the subsidized lunch reimbursement rate in three decades -- a false notion.
Apparently, no one in the press has actually bothered to read the rules governing the school meals program. If they had, they'd know that the disputed 6 cents are barely more than what the National School Lunch Program receives automatically each year by way of cost of living increases. This year, in fact, the reimbursement rate has already gone up 4 cents -- from $2.68 per lunch to $2.72 -- thanks to an adjustment in the Consumer Price Index.
Granted, school kitchens are broke and have been for a long time. According to the School Nutrition Association, schools that rely on the federal reimbursements to pay their expenses lose 35 cents on average with every lunch they serve, which helps explain why they feed kids sweetener-stuffed snacks instead of real food in order to comply with the USDA's calorie requirements.
The 6 cent increase would be laughable if it weren't so tragic. But more important in this stalled legislation is a provision that would, for the first time, give the USDA authority to regulate all foods sold in schools, possibly meaning an end -- finally -- to so-called "competitive foods," such as sugary drinks and candy in school vending machines and ice cream bars and fruit rollups in the deli line. That would go a long way toward addressing the obesity epidemic that Michelle Obama has pledged to end.
So I say, Keep your 6 cents. Let the nation's lunch ladies do what they've been doing for years that Congress can't -- live with what they've got. Congress can then continue doing what it does best -- spending money we don't have on wars we don't need. Somehow, the kids will survive.
