The majority of American children are not getting sufficient vitamin D from sun exposure, even in summer months, says a new analysis from leading researchers.
According to findings published in Environmental Health Perspectives, only children with type II skin (Caucasian) living in the northern US actually achieved the minimum daily dose of vitamin D and this only occurred in the summer months if they did not wear sunscreen.
The statistics were increased for children with all skin types living in the southern US in summer, but only children with the fairer skin achieved the minimum daily dose in spring.
“Our estimates suggest that many children may not get enough sun exposure to meet their minimum daily vitamin D requirements,” concluded researchers led by Dianne Godar, PhD, from the US Food and Drug Administration (FDA).
“However, additional research is needed to confirm our estimates, and improve our understanding of the net benefits and risks of sun exposure to children’s health.”
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
While our bodies do manufacture vitamin D on exposure to sunshine (UV-B radiation with a wavelength between 290 and 315 nm), the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
The researchers calculated average vitamin D production from sun exposure according to gender, age, skin type, clothing and the season for children living in the northern (45°N) and southern (35°N) US.
“Our estimates suggest that American children may not be getting adequate outdoor UVB exposures to satisfy their vitamin D3 needs all year, except some Caucasians during the summer if they do not diligently wear sunscreens except during beach vacations,” wrote Dr Godar and her co-workers.
The results challenge conclusions by the American Academy of Dermatology, which states that people will still make “ample” vitamin D3 (at least 1,000 IU/day) because they get plenty of “casual” (everyday) exposure to UV out side.
The role for supplements
The data clearly shows the importance of vitamin D supplements and fortified foods. Earlier this year, renowned vitamin D researcher, Michael Holick PhD, MD, Professor of Medicine at Boston University Medical Center and co-author on the new analysis, told NutraIngredients-USA.com that the most realistic approach to boosting the nation’s intake of vitamin D is for food manufacturers to increase the dose of vitamin D per serving.
According to Euromonitor, Functional foods, multivitamins and fish oil are an increasing threat to single vitamin D supplements.
The effects of deficiency
Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 diabetes.
The science supporting the muscle function of vitamin D, as well as the vitamin’s role in immune health, is sufficiently robust to have merited a positive opinion from the European Food Safety Authority’s (EFSA) Panel on Dietetic Products, Nutrition and Allergies (NDA). Despite such proclamations of support, many people across the world are not getting enough vitamin D.
Source: Environmental Health Perspectives
Published online ahead of print, doi:10.1289/ehp.1003195
“Solar UV Doses of Young Americans and Vitamin D3 Production”
Authors: D.E. Godar, S.J. Pope, W. Burgess Grant, M.F. Holick