Remember how good it used to feel, hanging out in the sun, letting your face acquire that nice, ruddy glow?
Then came all those depressing public health messages telling us that the sun was dangerous, that we should feel guilty about even the slightest tan.
Well, fellow sun worshipers, the sad truth is that as a general rule, we should still practice “safe sun” – including hats and sunscreen, especially for little kids – much of the time.
But there’s a new ray of hope – dare we say “sunshine?” – in the form of a modest but significant shift in medical thinking toward the view that SOME unprotected sun exposure may actually be a good thing, like 15 minutes or so a day in the summer for adult Bostonians who tan well, less for those burn easily.
“In my opinion,” says Dr. Robert Stern, chief of dermatology at Boston’s Beth Israel Deaconess Medical Center, “it’s probably true that for people over 40, even people who have had a non-melanoma skin cancer, we have oversold the idea of having to be sun-phobic. For them, modest exposure has little risk.” For kids, cautions Stern, it’s another matter – excessive childhood exposure to sunlight has been linked to later basal and squamous cell skin cancers, as well as to melanoma, a more serious form of skin cancer.
The rationale for the some-sun-is-good point of view, supported by a number of recent articles in medical journals, is that the vitamin D made in the skin in response to ultraviolet B radiation may protect against certain diseases, including cancer of the breast, colon and prostate.
Other diseases, most notably MS (multiple sclerosis), also show a “latitude effect,” that is, they are less prevalent among people in sunnier climes, though, as with cancer, whether this is truly due to vitamin D or to some other factor that varies by region such as diet, behavior or genetics is unclear. In rodents, high doses of vitamin D can actually prevent MS.
Sunlight may even be an effective treatment for some diseases. In a recent study published in the journal Lancet, Dr. Michael F. Holick, an endocrinologist and leading vitamin D researcher at Boston University School of Medicine and others showed that exposing people with mildly high blood pressure to UV-B can lower blood pressure, perhaps by correcting an underlying vitamin D deficiency.
Before we get in too deep here, let’s be clear. It’s vitamin D that has the real benefit, not sunlight per se, which means you can take vitamin D supplements, especially during the winter if you live at higher latitudes and especially if you have dark skin (which makes less vitamin D). By contrast, people in Florida typically make plenty of vitamin D all year in their skin. It’s very tough to get enough vitamin D from your diet unless you consume lots of fish liver oil, the flesh of fatty fish like salmon and fortified milk and cereals.
Actually, vitamin D is not a vitamin at all in the normal sense, but is really a steroid-like hormone made, after exposure to the UV-B rays from sunlight, from a precursor of cholesterol in the skin. After an inactive form of vitamin D is made in the skin, it is transformed in the liver and kidney to the active or hormonal form called 1,25 dihydroxy vitamin D. Indeed, several teams of researchers have recently found that the organs such as the breast, prostate and colon in which vitamin D seems to reduce cancer risk can also make their own stores of the vitamin’s active form, an important finding.
Like other hormones, vitamin D works by fitting into specialized receptors on cells in many organs of the body and has numerous biological effects, the most important one being to aid in the absorption of dietary calcium. When a person has enough vitamin D in his system, the intestines can absorb 30 percent of the calcium available in the diet; without enough vitamin D, this drops to 10 percent, notes Holick.
The consequences of insufficient vitamin D can be serious. When the body can’t absorb enough calcium from the diet, it steals calcium from the bones to restore proper levels in the blood, a process that weakens bones, often leading to osteoporosis. Low levels of vitamin D can also lead to weak and achy muscles, as well as generalized bone pain, symptoms often misdiagnosed as fibromyalgia.
Just as important as its effects on calcium and bone is the fact that vitamin D helps regulate many basic cell processes, notes Dr. David Feldman, an endocrinologist and vitamin D researcher at Stanford University School of Medicine. By acting on specific regions of DNA called vitamin D response elements, it helps control the biochemical signals that tell cells when to divide, when to stop dividing and when to die – all processes that are crucial in both normal and malignant cells.
In the early 1990s, for instance, researchers showed that adding the active form of vitamin D to cancer cells in the test tube inhibits their growth, a finding that has now been shown in breast, prostate and colon cancer cells as well as leukemic cells.
Currently, researchers at several labs around the country are testing whether a high dose, prescription form of vitamin D called calcitriol can slow the progression of prostate cancer in men with the disease. This treatment could increase the risk of kidney stones, says Feldman, but it’s promising enough that numerous drug companies are pursuing closely-related versions (or analogues) of active vitamin D that would be active against cancer without triggering kidney stones.
Vitamin D as a supplement has also been shown to be extremely effective at preventing Type I diabetes. A study by Finnish researchers published in Lancet last fall shows that vitamin D (2000 International Units a day) in infancy can reduce by 80 percent the risk of Type I diabetes 30 years later, perhaps because vitamin D slows the body’s immune attack on its own insulin-producing cells. This fits with data from mice showing that high doses of activated vitamin D will markedly reduce the risk of Type I diabetes.
But perhaps the most intriguing evidence of vitamin D’s importance comes from studies of sun exposure and cancer.
In the March 15 issue of Cancer, William Grant, by day an atmospheric scientist at NASA’s Langley Research Center in Hampton, VA and by night, an independent researcher, published a study showing that the geographic distribution of many cancers varies with UV-B exposure.
Since the early 1980s, Grant notes, scientists have been gathering evidence that some types of cancer – most notably, cancer of the breast, colon, ovary and prostate, as well as non-Hodgkin’s lymphoma – are higher in Americans who live in the least sunny regions.
“What I did was basically take two maps and put them together,” says Grant of his latest study. This showed that in addition to the cancers already known to vary with UV-B exposure, there appear to be many others (bladder, esophagus, kidney, rectum, stomach and uterus) that also increase as sunlight decreases.
In fact, more than 30,000 Americans die prematurely every year from cancer that may be attributed to low levels of UV-B exposure, Grant estimates.
Other researchers, too, have found links between sun exposure and cancer. In 1999, a team led by epidemiologist Esther M. John of the Northern California Cancer Center in Union City reported on a study of more than 5000 white women, 190 of whom developed breast between the time they were first interviewed by government researchers in the early 1970s and 1992.
The team correlated various measures of sun exposure and found that the women with the highest levels of sun exposure were the least likely to get breast cancer.
This March, researchers from the National Cancer Institute led by Dr. Michal Freedman, an epidemiologist, found that Americans living in sunny areas were significantly less like to die from (not just get) cancers of the breast, ovary, prostate and colon. Not surprisingly, her team found, high levels of sun exposure were also linked to the milder (non-melanoma) types of skin cancer, too.
The bottom line ? If you’re white, all it takes for your skin to make enough vitamin D is about 15 minutes a day in the sun, without sunscreen, at noon, says Holick. If you’re black, it may take considerably more than that. How much sun you should get depends on your skin type and sensitivity to sun – if you burn readily, you may only be able to tolerate five minutes in the sun, and that would be enough.
And if you’d rather just take vitamin D supplements? That’s fine – the general guidelines are 200 IUs a day if you’re 50 or under, 400 if you’re between 50 and 70, and 600 IUs if you’re over 70, says Tufts University epidemiologist Susan Harris. Some researchers even recommend 800 to 1000 IUs a day. (Since there’s almost no vitamin D in breast milk, Harris notes, breast fed babies living in less sunny regions of the country should probably take baby vitamins.
The risks of overdosing are small, adds Reinhold Vieth, a biochemist and vitamin D researcher at Mount Sinai Hospital in Toronto, who believes it would take tens of thousands of IU s for long periods to become a problem.. Still, to be on the safe side, many researchers suggest limiting vitamin D intake to 2000 IUs a day.
Judy Foreman is Lecturer on Medicine at Harvard Medical School and an affiliated scholar at the Women’s Studies Research Center at Brandeis University.. Her column appears every other week. Past columns are available onwww.myhealthsense.com.
SIDEBAR
Vitamin D and the Evolution of Skin Colors
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Vitamin D is part of one theory for the evolution of different skin colors among humans.
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Human beings arose with black skins in Africa and then migrated outwards from there. Black skin is rich in melanin, a pigment that acts as a natural sunscreen, protecting against sunburn.
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But, just like sunscreen of SPF 8 or higher, melanin reduces the amount of vitamin D the skin can make. That’s fine for someone in Africa who spends lots of time in the sun. Farther from the equator, however, people with light skin gain an evolutionary advantage. With less available UV-B, light skin probably evolved so that humans migrating northward would still be able to make enough vitamin D.
- Indeed, people who failed to make this adaptation would have had a difficult time reproducing. Insufficient vitamin D can lead to rickets, which causes defective bone growth. In women, this can mean such poor pelvic development that babies could not be borne – and the mother’s genes would not be passed on.