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Such results may lead to recommendations in certain countries of vitamin D supplementation for adolescents to help reduce the risk of osteoporosis
As South Africans, we are in the lucky position to be able to use our sunny climate to provide most of our vitamin D requirements. Therefore, such recommendations may not necessarily be applicable here.
“Vitamin D deficiency during childhood and adolescence might impair the acquisition of peak bone mass at the end of skeletal growth and maturation, thereby increasing the risk of osteoporotic fracture in later life,” explained the researchers from Saint Mary’s Hospital for Women and Children in Manchester.
Potential reduction of osteoporosis, a disease that affects over 75m people in Europe, the USA and Japan, has traditionally been a two-pronged approach by either attempting to boost bone density in high-risk post-menopausal women by improved diet or supplements, or by maximising the build-up of bone during the highly important pubescent years.
About 35 percent of a mature adult’s peak bone mass is built-up during puberty.
But the new study, published in the Archives of Disease in Childhood (Vol. 91, pp. 569-572), suggests that the burden of osteoporosis could increase in the future with the finding that over 70 percent of the teenage girls who took part in this study were vitamin D deficient.
The research study
The research, led by Dr Zulf Mughal, recruited 51 teenage girls with an average age of 15,3. Fourteen girls were white, and the other 37 were non-white. Dietary intake of vitamin D and calcium were assessed using food frequency questionnaires, and skin exposure to sunlight was also calculated based on typical everyday clothing cover.
The girls also had blood samples taken to measure levels of calcium and 25- hydroxyvitamin D (25(OH)D), the non-active ‘storage’ form of the vitamin.
The researches report that 73 percent of the girls (37 girls) were vitamin D deficient, with levels of 25(OH)D below 30 nanomoles per litre of serum.
Worryingly, nine girls (17 percent) had levels below 12,5 nanomoles per litre. These low levels are typically associated with rickets and osteomalacia.
Non-white vs. white girls
It was also found that, on average, non-white girls had significantly lower levels of 25(OH)D than white girls, and this was related to sunlight exposure and not dietary intake.
“Avoidance of exposure to sunshine for religious and cultural beliefs that encourage wearing of concealing clothing and restriction of outdoor activities has previously been reported as a risk factor for vitamin D deficiency in Saudi Arabian adolescents.
“Increased skin pigmentation is a further factor that might explain the difference in vitamin D status of white and non-white girls in our study,” wrote the researchers.
In an accompanying editorial, Professor Nick Bishop, from the University of Sheffield, warned that: “failure to supply an essential nutrient during a period of rapid growth and development is likely to result in problems across the population as a whole”.
“Further studies are required to determine if subclinical vitamin D deficiency… results in reduced bone mass accrual around puberty, and whether vitamin D supplementation can help to prevent this,” concluded the researchers.
Vitamin D is synthesised in the body on exposure to sunlight and only small amounts can be obtained from food.
More sun exposure for some
However, recent studies have shown that sunshine levels in some northern countries are so weak during the winter months that the body makes no vitamin D at all, leading some to estimate that over half of the population in such countries have insufficient or deficient levels of the vitamin.
UK researchers recently proposed 10 to 15 minutes of unprotected exposure to the midday sun as a good source of the vitamin. In the US, where over 1,5 million people are diagnosed with skin cancer every year, experts are pushing supplements, claiming recommendations for sun exposure are “highly irresponsible”.
The best source could be from fortified foods and supplements. - (Decision News Media, August 2006)
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