During summer, we avoid direct sunlight, slathering ourselves with sunscreen, wearing big hats and dressing like Bedouins. We’ve been warned about various skin cancers and the accelerated aging that results from too much pleasure in direct rays. Many of us work at computers all day and play on computers when we’re not working. We don’t get out much, especially now, in the winter winds and lack of direct sunlight.
But exposure to sunlight is necessary for the production of vitamin D. We’ve all learned that this element helps maintain bone health, but it is also an important component in immune system function – something to consider as flu season descends.
Vitamin D deficiency
When sunlight comes into contact with a precursor sterol in the outer skin a complex series of transformations results in the synthesis of vitamin D. As long as we have sufficient access to the sun, it’s not necessary to worry about getting it in our food. A good thing, as not many foods contain vitamin D.
With vitamin D added to milk in this country, severe deficiency is relatively rare. But when it occurs in infants and children, the result is a failure of bone to mineralize, a condition known as rickets. The bones grow, but they’re not strong. Weight bearing bone tends to bow, fontanels in an infant’s skull will be slow to close, and the rib cage can become malformed due to pulling of the diaphragm. In adults with severe deficiency, bone mineral is lost causing pain and osteomalacia or soft bones. Insufficient blood (serum) levels of vitamin D can cause muscle weakness, pain and fatigue in children and adults.
A number of tests have indicated that low serum levels of the vitamin can pre-dispose people to infection.
In April 2005, John J. Cannell, a psychiatrist at a maximum-security forensic psychiatric hospital for men in central California noticed during an outbreak of a particularly virulent strain of influenza that the men on his ward seemed to stay healthy while one ward after another all around his was locked down. His men had been exposed to those who become ill and yet stayed free of the disease. He thought it was luck until he read an article in the July 2005 journal of the Federation of American Societies for Experimental Biology reporting that vitamin D boosts production of one of the antimicrobial compounds in white blood cells that helps defend the body against a number of different types of germ.
Cannell had noticed when he tested their blood that his patients, like most people in the industrialized world, had low levels of vitamin D. He put them on high supplemental doses. This raised serum levels of the anitmicrobial peptide cathelicidin and that, apparently, is what protected them from the flu.
When Cannell went through the literature he found that cathelicidin targets and destroys several species of bacteria, viruses, and fungi. He concluded that vitamin D deficiency may underlie a vulnerability to infections caused by those microbes. He and his colleagues reported their findings in the December 2005 Epidemiology and Infection. Subsequent lab tests have found that nothing excites the gene responsible for cathelicidin production like vitamin D.
Findings of tests conducted by Departments of Nutritional Sciences and Pathobiology of Pennsylvania State University also demonstrated the importance of vitamin D as an important immune system regulator. It was shown to inhibit the development of several autoimmune diseases, including inflammatory bowel disease (IBD). The results were most impressive when the vitamin was administered along with a calcium rich diet.
In addition to flu and other diseases caused by viruses and bacteria targeted by cathelicidin, vitamin D deficiency has been linked to tuberculosis susceptibility. (Remember those 19th century novels in which people with TB were sent to asylums in sunny places?) People with dark pigment are more likely to be vitamin D deficient than light skinned people and, globally, they are also more susceptible to TB.
As a result of their investigations, Cannell’s team postulated that lower exposure to ultraviolet light may be an important factor in the higher incidence and severity of colds, flu, and other respiratory diseases during the winter.
Sun-bathing
The application of sunscreen with an SPF factor of 8 (and who uses such a weak product these days) reduces production of vitamin D by 95 percent. In temperate latitudes there is insufficient UVB radiation available for vitamin D synthesis from November to early March. But generally speaking, as little as five to 10 minutes of sun exposure on your arms and legs, or face and arms, three times weekly between 11 a.m. and 2 p.m. during the spring, summer, and fall – sans sunscreen – should provide a light-skinned individual with adequate vitamin D allowing enough left over for use during the winter. The risk of skin damage at this exposure is minimal.
Food sources
It’s hard to find a good food source. You can find it in some fatty fish (mackerel, salmon, sardines), fish liver oils, and eggs from hens that have been fed vitamin D. In the U.S., milk and infant formula are fortified with vitamin D so they contain 400 IU (10 mcg) per quart, the FDA minimum daily requirement,. Some cereals and breads are also fortified with vitamin D. Orange juice fortified with vitamin D is widely available. And, of course, you can get vitamin D supplements.
Too much of a good thing?
It’s indeed possible. Before you decide to take supplements prophylactically, see your doctor. Have a complete blood count (CBC) to determine your serum levels of vitamin D and then you and your doctor can decide upon a reasonable dose ... if you need it.
Vitamin D toxicity can result in abnormally high calcium levels (hypercalcemia), which could result in bone loss, kidney stones and calcification of organs like the heart and kidneys if untreated over a period of time. Because the results of hypercalcemia are so severe, the Food and Nutrition Board established a very conservative upper limit of 2,000 IU/day (50 mcg/day) for children and adults. Vitamin D toxicity is unlikely in healthy people, but, as with any supplement, it’s still best to consult your primary care practitioner before buying it. One thing is sure: you definitely can’t get it from spending 10 minutes or so in the sun. Bundle up, take a walk and enjoy the sun.