Seek out the light
That light is the best source of vitamin D, better even than fatty fish or supplements. UVB rays induce a substance in our skin called 7-dehydrocholesterol to produce vitamin D. Then it makes a beeline for the liver and becomes the prohormone calcidiol, and then to the kidneys, when it changes to calcitriol, the active hormone. After that it goes into the bloodstream and affects metabolism of phosphorus and calcium to strengthen bones. Calcium also fortifies muscles, including the heart muscle. The calcitriol also may go to the tissues of body organs and the immune system. Receptors for it are found in various glands, the heart and brain.
Some studies have recommended that at least twice a week you should let the sun kiss your skin on face, arms, legs or back for about five minutes to half an hour, between 10 a.m. and 3 p.m. Not surprisingly, the American Academy of Dermatology advises that sunscreen be part of the picture. Of course getting out there for a walk or run, even if just across a big parking lot, will add myriad other benefits. If you live closer to the equator or at a high elevation you may get more of the benefit of sunshine. In summer, obviously you get more, and weather patterns like cloud cover and protective gear from hats to that sunscreen can reduce your exposure.
The more melanin in your skin and the darker it is, the less benefit you get from this source. Although childhood rickets is much less common than it once was, most cases are in breastfed African-American babies, in part because they aren’t getting the supplemental vitamin D in formula and their mothers may have low levels.
The sun is seen as evil; it makes you wrinkle or get skin cancer, so many of us limit it or avoid it all together. The sickly and the elderly may spend more time indoors and not get its benefits.
Good food sources
Besides tuna, mackerel, sardines and salmon as good sources, mushrooms, especially dried shiitakes like you find in Chinese cooking, are good, too. So are products that may have it added, from milk (since the 1930s) to orange juice to cereals, and always infant formula. There’s a little bit in egg yolks and beef liver. Then of course there’s cod liver oil if you don’t mind the taste or the extended fish burps. I hear some modern versions in capsule form avoid that.
