Remember how, in “The Hitchhiker’s Guide to the Galaxy,” the answer to all things turned out to be the number 42?
Here on planet Earth, the real number is different: 37.
The 37th parallel is the latitude line below which people’s skin gets enough sunshine to produce a healthy amount of vitamin D. That’s a natural process, triggered when ultraviolet radiation hits a substance in the skin called 7-dehydrocholesterol. The resulting chemical travels to both liver and kidneys, picking up oxygen and hydrogen, preparing for work.
Above the 37th parallel, sunshine is weaker, especially in winter. According to a growing body of science, this leaves local people more prone to vitamin D “insufficiency,” which means a little too little, or “deficiency,” which means lacking a lot.
Clark County is on the 45th parallel. Does that mean we should be popping vitamin D capsules?
The answer is a resounding yes for many, according to Dr. Caroline Tse, an associate professor of neurology at the Oregon Health & Science University School of Medicine. Because vitamin D is naturally present in few foods, a daily D supplement probably is a fine idea for most of us, Tse said.
What D does
Why D? Chiefly because it’s essential for strong bones and muscles, Tse said. Fortified cereal, milk and juice cartons have been stressing that point since the 1930s, when D was added to prevent rickets (soft, brittle bones) in children.
But there’s a lot more to learn about vitamin D, according to Harvard Medical School. Tissues all over the body have vitamin D receptors, and the cardiovascular, digestive and immune systems seem to rely on D in ways not fully understood. Vitamin D may even help fight prostate, breast and other cancers.
Meanwhile, there’s also evidence that a lack of vitamin D can cause numerous problems. Childhood rickets is mostly gone from the U.S., but the adult version, osteoporosis, is on the rise. Low vitamin D can also cause joint and muscle pain, increased pain sensitivity overall, muscle twitching and muscle weakness.
Tse, whose primary specialty is sleep medicine, added that low vitamin D has also been associated with sleep difficulties, fatigue and depression.
But “association” is where the science gets murky. Looking to vitamin D as a specific cure for the blues is not supported by evidence, Tse said.
“Some studies have found links between low blood levels of vitamin D and an increased risk of depression,” is the official word from the National Institutes of Health, Office of Dietary Supplements. “However, clinical trials show that taking vitamin D supplements does not prevent or ease symptoms of depression.”
Confused? Us too.
“We haven’t been able to find that vitamin D is that cure for depression,” Tse said.
D is for deficiency
The older you are and the more melanin your skin contains, the more prone you are to vitamin D deficiency. (Melanin, or skin pigment, functions like a shade, blocking sun absorption.) Distance from the equator is a risk factor too. Most of the U.S. is above that key 37th parallel, which marks the southern borders of Utah and Colorado and runs through Death Valley, Calif.
In 2005-2006 and again in 2011-2012, National Health and Nutrition Examination Survey studies conducted by the Centers for Disease Control and Prevention came up with similar results: about 40 percent of all American adults have a vitamin D deficiency. For Hispanics the number is closer to 60 percent and for Blacks it’s 82 percent. A smaller study of older Americans found that a whopping 85 percent had a vitamin D deficiency.
“There are some pretty staggering statistics associated with vitamin D deficiency,” Tse said.
(There’s also ongoing debate about what really constitutes deficiency and how many people really have it, a survey of academic and popular-science articles shows. Some say the deficiency alarm is overblown.)
Why are older folks at greater risk? In addition to aging metabolism, Tse said, they just don’t get outside and absorb sunshine as much as they used to.
D a day?
The National Academy of Sciences recommends vitamin D intake of 600 units per day for nearly everyone. For babies 1 and younger, the recommendation is 400 units. Over 70, it’s more: 800 units. People remedying a deficiency may take a lot more — 2,000 or even 4,000 units — as they work to increase the amount of vitamin D in their blood to a healthier level, Tse said.
While it’s hard to get vitamin D through food alone (which is why it’s added to milk, cereals, juices and other foods), the Pacific Northwest is a good place to try. Salmon, tuna, sardines and other fatty fish are excellent sources of vitamin D. So are egg yolks, common mushrooms and beef liver.
And that’s about it for dietary vitamin D sources. That’s why D capsules seem like one bright spot in the otherwise shady world of vitamin supplements, a multibillion-dollar industry. (In 2013, three large studies reported in the Annals of Internal Medicine, and summarized in Scientific American, found no clear benefit and some risk of harm in multivitamin and mineral supplements.)
Vitamin D appears to be different. The same medical establishment that dismisses multivitamins is recommending amounts of D per day that can only be easily achieved through supplements.
“Personally I don’t think there’s any harm in bumping up to 2,000 units or even 4,000, especially during winter,” Tse said. “The National Academy cautions against more than 4,000. There can be some risk of toxicity.”
People diagnosed with severe deficiency may go much higher. If you wonder about your vitamin D level, ask your doctor. Screening is as simple as a blood draw.
Since sunlight triggers D production, and sunlight is what we lack in winter, doesn’t it make sense to replace it with one of those morning-light “happy lamps,” the super-bright kind that aim to combat winter depression, otherwise known as Seasonal Affective Disorder?
No, Tse said. SAD lamps produce a different spectrum of bright light. They specifically filter out the ultraviolet radiation that triggers vitamin D production in the skin. SAD lamps do not stimulate vitamin D production in the skin, Tse said.
But light therapy might just be the winter-depression treatment you’re after, she added. SAD lamp light works by emitting powerfully bright light that enters your eyes (obliquely, without blinding you), releasing serotonin (the happy hormone) and helping reset your body clock so you feel awake in the morning, not sad and sluggish. Talk to your doctor about starting light therapy.
What about tanning beds? Don’t they put out UV light? They sure do, but medical professionals frown on them because they pose serious risk of skin cancer. Don’t go to a tanning bed for vitamin D, Tse said.
Instead, Tse said, try this simple recommendation: Just go outside for at least 15 minutes a day. No problem if it’s cloudy, since a cloudy day in the Pacific Northwest is still far brighter than your typical artificially lit indoors, Tse said.
If it’s sunny, don’t skip on sunscreen, which protects against skin cancer and has been shown to have minimal effect on vitamin D production. For best health, Tse said, down a D, apply some sunscreen and go outside.