If the sun burned out and all the cows died, pretty soon we'd all be walking around with rickets.
Happily, the sun is still shining - that's pretty much a given in this heat - and the pastures are still populated with grazing bovines. But rickets is still making a slight comeback, particularly among infants and young children. The journal Pediatrics estimates 70 percent of American children are D-ficient. Not to the point of complications but still enough to get the attention of the medical profession.
Other symptoms of vitamin D deficiency occurring in young people, adults and seniors include "achy bones, achy joints, muscle fatigue and muscle weakness," says Dr. Steven Joyal, vice president of scientific affairs and medical development for the Life Extension Foundation in Fort Lauderdale, Fla. "They are somewhat unspecific, but all are signs of a vitamin D deficiency."
But wait, there's more. According to the National Institutes of Health's Office of Dietary Supplements, vitamin D also prevents certain cancers; prevents diabetes, hypertension, glucose intolerance and multiple sclerosis; wards off osteoporosis (with calcium) in older adults and "modulates neuromuscular and immune function and reduction of inflammation" (in other words, colds, fever and flu).
There are also studies that indicate D-deficient diets are associated with lactose intolerance and milk allergies.
Vitamin D comes to humans in dairy products, fatty fish (salmon, catfish, tuna), broccoli, mushrooms and, mainly, sunshine. That's why it's called "the sunshine vitamin." But over the years, we've reduced our milk intake because of alarms about animal fat, we've cut down on salmon because of mercury levels, and broccoli, parsley and mushrooms, well, "That's what food eats," as one disgruntled 12-year old boy was recently heard to say at the dinner table.
And as for that sunshine, just one word: melanoma.
Skin cancer is the most common form of cancer in the U.S., according to the Skin Cancer Foundation. More than 3.5 million cases in 2 million people are diagnosed each year (melanoma has a tendency to recur if not successfully treated). One in five Americans will develop skin cancer.
Each year, there are more new skin-cancer cases than there are cases of cancers of the breast, prostate, lung and colon - combined. The incidence of melanoma is rising faster than any of the seven other leading causes of cancer. One person dies of melanoma every hour.
Our educated cultural response has been to shield our vulnerable skin - and all of it is vulnerable - from the sun's rays with sunblock and sunscreens (see sidebar). Those chemicals, even the least expensive ones, are very effective in reducing the amounts of harmful UVA and UVB sunlight that penetrates the skin, some by as much as 97 percent. But there is little argument that those chemicals also reduce the amount of vitamin D that's produced by the skin.
Vitamin D production is stimulated when ultraviolet light B - UVB - is absorbed in the skin. But when it's blocked, the production goes down.
Dangerously so? "There's a lot of discussion in the medical community," Joyal says.
Dr. Bess Dawson-Hughes, director of the Bone Metabolism Laboratory at Tufts University, told The Boston Globe that "10 minutes a day of sun exposure to the face and arms without sunblock protection" is enough to trigger vitamin D production without increasing skin-cancer risk. In his book The UV Advantage, Dr. Michael F. Holick at Boston University recommends "five to 15 minutes a day a few days a week" of sunlight exposure.
The idea is to not overdo it.
"A tan is a sign of sun damage; it's the body's reaction to sunlight as it tries to protect the skin from the sun," Joyal says. "The idea of a 'safe tan' is a myth."
"We know that 90 percent of skin cancers are caused by the sun and that the sun and tanning booths are known and documented human carcinogens," says Dr. Mona Gohara, assistant clinical professor at the Department of Dermatology at the Yale School for Medicine.
Gohara believes it's best not to take the risk of going out in the sun without sunscreen. "UVA and UVB are still coming through even if you are being diligent with sunscreen."
And being diligent means this: "You are supposed to put on, which very few people do, the equivalent of a shot glass of sunscreen over your entire body every two hours."