Food Becomes You - Good News for Sun Lovers

The sun has gotten bad press in recent years. Judging by the constant admonitions from medical professionals and the media to stay out of the sun, cover up, and lather on the sunscreen, you'd think the sun was toxic rather than essential to life.

Being a sun-worshipping Mediterranean type, I love the feeling of hot rays on my skin. So I was happy to discover evidence that modern medicine's fear of the sun may be a bit excessive.

Sunlight is our major source of vitamin D. Vitamin D is not actually a vitamin, but a prohormone. Sunlight shines in a range of wavelengths, including the ultraviolet rays UVA, UVB, and UVC. When UVB rays penetrate the epidermis they are absorbed by a metabolite of cholesterol and converted into vitamin D (calciferol). Calciferol is then metabolized in the liver to calcidriol and converted into an active hormone (calcitriol) in the kidneys.

Vitamin D's best-known function is the regulation of the amount of calcium and phosphorus in the circulation and the control of bone mineralization. Not so well elucidated are its functions as an immune system regulator. Vitamin D may significantly reduce the incidence of inflammatory autoimmune reactions. It also regulates the production of some enzymes, hormones, and neurotransmitters.

Humans evolved near the equator, where they spent their lives outdoors, barely clothed. In this Neolithic era, obtaining adequate vitamin D was not a problem. But once humans moved northward, indoors, and into crowded cities, rickets (a bone softening disorder caused by vitamin D insufficiency) became common. This crisis reached epidemic proportions in northern industrial cities in the nineteenth and early twentieth centuries. Fortification of dairy products and cereals did a lot to correct the problem, but recently evidence has surfaced showing that vitamin D deficiency is once again on the rise.

Indoor lifestyles and the use of sunscreen (which blocks UVB) rays are probable causes. In the United States, UVB rays are significantly present only at midday during the summer - precisely the time we're warned to avoid the sun! Glass, clouds, smog, and fog limit the flow of UVB light. Many common drugs interfere with vitamin D absorption, including Dilantin, mysoline, and phenobarbital for seizures; corticosteroid; Tagamet (for ulcers); heparin, and the anti-TB drugs INH and rifampin. Obese people don't process vitamin D from sunlight as well as thinner people, perhaps because as much as 50% of the D is being sequestered in body fat. Some people are more genetically susceptible to vitamin D deficiency than others, with darker-skinned folks at high latitudes particularly at risk. A study of veiled Arabic women showed they also have very low circulating vitamin D levels.

While sunlight is undeniably a cause of skin cancer, it is not the only factor. UVC rays, found in fluorescent and halogen lights, may be major carcinogens. Also, burns produced by sudden extreme sun exposure (such as a week in Jamaica in the midst of a cold northern winter) are far more conducive to cancer than consistent moderate exposure.

Obviously vitamin D deficiency causes bone disorders, including dental problems and loss of hearing in older people due to the softening of the inner ear bone. Several autoimmune disorders have been linked to insufficient D. The most dramatic evidence exists for multiple sclerosis. Some genetically susceptible people may not get enough D during early childhood, when fatty myelin sheaths form around the nerves. In later life, these people are more prone to developing multiple sclerosis. Vitamin D deficiency has also been linked to sarcoidosis, both childhood and adult-onset diabetes, and Crohn's disease. There may possibly be a connection to neurological disorders including Alzeheimer's, Parkinson's, depression, and learning disabilities. Deficiency may possibly be a contributing factor to colon, breast, and prostate cancer.

Vitamin D is fat soluble, and can accumulate to toxic levels in the body. High levels are also associated with a host of problems: bone loss, heart disease, kidney stones, poor appetite, weight loss, headache, and depression. Chronic high vitamin D levels can cause irreversible damage to body tissues.

The only way to monitor vitamin D levels in the body is through regular blood tests for its active form. Unfortunately, toxic levels may not show up in the bloodstream until they've been wreaking havoc for 2-3 years. The optimal daily dose of vitamin D is controversial. The RDA lists it at 200 IU for those under 50, 400 IU for those 50-70, and 600 IU for those over 70 (at highest risk for osteoporosis). Most medical professionals don't recommend dietary supplements any higher than 800 IU, but a few recommend 1000 IU, and a very few up to 4000 IU.

The best source of vitamin D is sunlight. It's the natural way, most readily absorbed and regulated by the body. Get outside, every day, particularly in the summer, and don't be afraid to expose yourself to 10-20 minutes of midday sun. (Obviously lighter skinned people should exercise more caution than darker ones.) Foods are generally speaking not a great source of vitamin D. In this day and age, fortified foods such as milk and cold cereals are your best bet. Vegans can use fortified soymilk and margarine and should keep in mind that grains contain phytates, which in large quantities interfere with vitamin D absorption. Cold water fish such as herring are decent sources. Cod liver oil, which many of our parents and grandparents choked down, is an excellent source of D but also contains potentially toxic quantities of vitamin A. Sufficient fat (10% of the diet) is needed for adequate absorption, as well as pantothenic acid (not a problem if you eat a varied diet of unprocessed foods), calcium, and magnesium. Many calcium supplements come packaged together with a vitamin D supplement.