It was a beautiful summer day, and the Boston Public Garden was filled with walkers, people feeding the ducks and squirrels and/or listening to the weekend saxophone player near the Swan Boats. But mostly? People were soaking up the sun to remove some of the pallor from six months of relatively sunless days. Most women were wearing typical summer outfits: sleeveless or short sleeve shirts, shorts, or short skirts. These outfits exposed enough skin to allow the ultraviolet rays to catalyze the process of making vitamin D. Vitamin D is essential because it supports calcium absorption from the intestinal tract into the body. Without calcium, bone tissue cannot be made. In fact, insufficient vitamin D is responsible for rickets, a childhood disease first described in the 17th century. Bones fail to grow and mineralize sufficiently and as a result, they are soft and deformed. Adults need vitamin D as well to prevent osteomalacia, a weakening of the bones and the muscles to which they are attached. Osteoporosis, a disease in which fragile bones break extremely easily, is also linked to insufficient amounts of this vitamin.
But why should vitamin D levels ever be insufficient? It is provided, at no cost, from the effect of sunshine on the skin.
But some, indeed many, cannot rely on the sun to make this important nutrient.
Consider again the scene in the Boston Public Garden. To be sure most of the people have their arms, legs, and faces (and a few torsos) exposed to the sun. But here and there women are walking about or sitting on park benches with only the area between the bridge of their nose and the top of their eyes exposed to the sun. They are wearing a niqab, a small cloth, that covers all of the face except the eyes, in addition to a scarf that covers their hair and neck. A heavy robe (it cannot be see-through), or long sleeves and pants cover other parts of the body that otherwise might be exposed to the sun. And it is not only the Moslem women who are so covered up. So are ultra-Orthodox Jewish women and their daughters enjoying an afternoon stroll. Thick tights or stockings, long sleeved, high-necked blouses, long skirts and wigs or scarves cover their hair and limit the amount of skin exposed to the sun only to the hands, small neck area and the face.
Such concealing clothing has a negative impact on vitamin D levels. Several studies among Moslem communities whose women wear the most extreme style of Islamic dress have found them to be chronically deficient in vitamin D. (Mishal, A.A., Effects of Different Dress Styles on Vitamin D Levels in Healthy Young Jordanian Women. Osteoporosis International, 2001. 12(11): p. 931-935.)
The same deficiency has been observed in Dearborn, Michigan among the Arab-American female population. Veiled women had levels of vitamin D well below the minimum necessary to prevent rickets in their children (their breast milk would have insufficient vitamin D) and osteomalacia. (Hobbs, R., et al., Severe Vitamin D Deficiency in Arab-American Women Living in Dearborn, Michigan. Endocrine Practice, 2009. 15(1): p. 35-40.)
In one study, 40% of ultra-Orthodox women whose vitamin D levels were tested in a Tel Aviv hospital were found to be deficient in the nutrient. (Siegel-Itzkovich, J, Ultra-Orthodox Jewish women at risk of vitamin D deficiency British Medical Journal 2001 ;323, 10). The effect of skin concealment on vitamin D levels was also found among adolescents in an ultra-Orthodox community in Brooklyn, due to a combination of their clothing, and that boys are indoors studying from early morning to evening.
Vitamin D deficiency can be found among many other groups as well, due to inadequate sun exposure in general. The elderly and others unable to go outside because of sickness or lack of mobility, workers with schedules restricting outside access during the work week, people with skin conditions necessitating avoidance of sunlight, and those who live in geographical areas with weather inhospitable to outdoor exposure…they also suffer. And of course, using sun block is going to prevent most ultraviolet rays from reaching our skin. Interestingly however, most people (according to dermatologists) do not use enough sunblock, or do not put it so thoroughly over themselves so as to block out some sun exposure. Air pollution also reduces significantly the amount of ultraviolet radiation that reaches the skin.
How long one has to be exposed to the sun varies depending on who gives advice. Dermatologists will probably say avoid sun completely, but other medical folk more concerned with bone breakage and the effect vitamin D deficiency may have on immune function will suggest a spectrum of 5-10 minutes to half an hour daily. Time spent outside walking to the mailbox or walking your child to school does not fit into these calculations. And of course skin exposure to the sun is seasonal and weather dependent. The good news is that Vitamin D is stored in our liver, so try to think about it like banking money in July for Christmas shopping in November in that vitamin D made in the summer should be around in the winter.
Since it is unlikely that people with limited or even non-existent exposure to sunlight are going to be able to alter their situation, or that most of us will risk skin cancer by avoiding sunblock and frying ourselves on the beach? The alternative is to obtain vitamin D from food sources or as a supplement. Having your vitamin D levels measured might be worthwhile if you suspect that you are deficient.
The daily requirement is 600 IU until age 70 when the requirement increases to 800 IU. The best source is the worst tasting and smelling: cod liver oil. Salmon and swordfish are pretty good sources, while canned tuna in water is marginally good. Vitamin D fortified orange juice, milk, yogurt and even ready-to-eat cereal are reliable sources, but may not be eaten in large enough amounts to meet daily needs. It is important to check labels to see how many servings are needed to get l00% of the daily quota. Supplements that provide the recommended daily allowance should be taken if neither sunlight nor food are going to give the body the vitamin D it requires.
Weakening bones are silent—until they break. Don’t let covering up the skin cover up vitamin D deficiency.