I have written about low bone mineral density in infants and the high incidence of probable intrauterine rickets before.
I also reported on a prospective cohort study of vitamin D and stress fractures in adolescents.
Recently, Doctors Winzenberg and Jones of the Menzies Research Institute Tasmania in Australia reviewed the literature on vitamin D and bone health in children and adolescents.
Here’s a quick breakdown on what they found. First, on vitamin D deficiency:
- Vitamin D deficiency is common in children from most countries and some studies show the prevalence of vitamin D deficiency is higher in late adolescence.
- In a review of 186 cases of rickets in the USA, 83% were in Blacks and 96% were in breast-fed infants. Only 5% of breast-fed rachitic children received vitamin D supplementation.
On fractures, bone mass and osteoporosis:
- Childhood fractures are common, as common as fractures in young to middle age adults, and low bone mineral density is a risk factor for childhood fractures.
- Low peak bone mass is as important as later bone loss in the development of osteoporosis. Estimates of the age at which peak bone mass is reached vary widely, but studies have shown that 80–90% of peak bone mass is reached in the late teenage years.
- Computer models have reported that a 10% increase in peak bone mass would delay the onset of osteoporosis by 13 years.
- In two studies of forearm fractures of African American children in Washington D.C, 59% were vitamin D deficient (<20 ng/ml); the majority (58%) of forearm fractures resulted from minor trauma, and 25(OH)D levels were slightly but significantly (47% vs. 41%) more likely to be deficient (< 20 ng/ml) in children with fractures.
- The infants of adolescents consuming vitamin D enriched dairy products four times a day had better new born total body calcium scores than did pregnant adolescents consuming the same amount of calcium as supplements. However, this does not prove it was the vitamin D; milk may have nutrients, other than vitamin D and calcium that maintain bone.
- In a study of 198 children, maternal vitamin D levels were slightly but negatively associated with children’s bone mineral content at age 9 (p = 0.03) respectively.
Surprisingly, most studies show that that vitamin D supplementation has little or no effect on bone mineral content of breast-fed infants. As breast milk is almost always low in vitamin D, there must be something in breast milk that protects the bones.
Similar to the recent USPSTF’s recommendations in older adults, a Cochrane meta-analysis of six randomized controlled trials showed low daily doses of vitamin D had little effect on bone mineral density in children or adolescents.
In my opinion, this may be because bone is high on the list of what Doctors McCann and Ames call the triaging ability of the body to route nutrients to those functions required for short-term lifesaving functions. Bone is probably maintained at relatively low vitamin D levels because bone serves as a reservoir for the calcium needed to maintain blood calcium levels, which, if not done, may result in immediate death. I wrote about something similar in 2006, using a mountain pool analogy.
Think of vitamin D as contained in a mountain lake with streams and pools beneath the lake. Only if the “maintain serum calcium and the bone reservoir of calcium” uppermost lake is full does vitamin D flow over to fill up lower pools, such as the “prevent autoimmune diseases” pool lower down on the mountain. Thus higher blood vitamin D levels will be required to prevent autoimmune diseases than to maintain serum calcium and bone calcium. That is, the functions of a nutrient are restricted during shortage and those functions required for short-term survival take precedence over those that prevent chronic disease.
The authors conclude,
“From the perspective of bone health, the role of vitamin D in preventing rickets is clear and it is also clear that there is great potential to improve bone outcomes through maintaining adequate vitamin D levels throughout childhood and perhaps even in utero. However, the evidence base to date is limited, particularly for interventions in pregnancy and infancy. Robust evidence to accurately quantify the effectiveness of supplementation is lacking at all stages of childhood. The available data suggest that benefits are likely to be maximized by targeting children with vitamin D deficiency, and this population should be a focus of future research.”