Around the world, pediatricians, researchers, and parents have noticed a worrying trend. Girls are entering puberty, and experiencing their first menstruation, much earlier in life.
What’s the right age? There’s no hard and fast rule. But if we want to know what used to be normal, cross-cultural and historical studies supply the answer.
For most of human history, girls didn’t have their first menstrual periods until their mid-teens.
Nutrition and exercise played a big role. A girl needs to accumulate a certain amount of body fat to begin cycling.
Modern studies confirm that hunter-gatherer girls are very lean and athletic…and they begin cycling around the age of 16. In some hunter-gatherer groups, the lifestyle is so demanding that adult women may sometimes stop cycling.
So researchers have looked for links between body fat and early menarche (the commencement of menstruation). And the results seem clear. Young girls with higher BMIs (“body mass indices”) are more likely to experience early menarche.
That’s interesting and helpful. But what about all the relatively slim girls who are experiencing early menarche? There’s probably more going on, and a new study suggests another answer:
Maybe vitamin D deficiencies trigger early menarche in girls.
Eduardo Villamor and researchers from the University of Michigan School of Public Health tested blood levels of vitamin D in 242 girls (aged 5-12 years) from Bogota, Colombia. They followed the girls for about 30 months to see who experienced menarche–and when.
The results suggest a link. After controlling for a girl’s age and BMI, the probability of early menarche was twice as high in vitamin D-deficient girls. Overall, girls low in vitamin D experienced their first period about 10 months early than other girls did.
Of course, we can’t conclude that vitamin D deficiency causes early menarche. Or that you can prevent menarche by treating girls who have vitamin D deficiency. We need more studies to establish causation.
But the new study gives us another reason to make sure our kids are getting enough vitamin D.
According to recent studies, most American kids aren’t getting enough. And it’s a global trend. Worldwide, about 1 billion people are vitamin D deficient or insufficient (where “insufficient” indicates a less severe condition).
When children are vitamin D deficient, their bone health may suffer. Vitamin D deficiency may also put them at higher risk for developing autoimmune diseases, cardiovascular disease, cancer, type II diabetes and infectious diseases.
Why the pandemic?
Vitamin D is produced in the skin in response to sun exposure. So indoor lifestyles–and legitimate health concerns about excessive sun exposure–are probably to blame.
And children are more likely to develop vitamin D deficiency if they live at high latitudes–especially if they have dark skin.
In one study, non-hispanic Black adolescents had 20 times the risk of low vitamin D levels compared with non-hispanic White adolescents.
So it’s a good idea to talk to your doctor about vitamin D. And don’t try to make guesses and treat a condition on your own. Too much vitamin D is harmful, so you shouldn’t give your child over-the-counter supplements without first consulting your physician.