Good Medicine: The Winter Clouds Are Rolling In—and Your Vitamin D Is Going Down. Are You at Risk?

 

The overcast skies of autumn signal a change to come inside us: Our vitamin D levels drop. The clouds block the sun’s ultraviolet rays, which, through a biochemical reaction in our skin, create 90% of the D we need. (The rest comes from food.) This essential vitamin reduces inflammation, aids our glucose metabolism, keeps our nervous system functioning, and regulates the blood calcium necessary for bone and muscle health. Luckily, two-thirds of American adults have enough D stored up to last through the cold, gray, bundled-up days of winter.

But one-third of adults in the United States are chronically low in vitamin D and can suffer a significant deficiency come wintertime. This includes those who habitually avoid the sun or use sunscreen year-round—SPF 30 blocks virtually 100% of UV rays—and those over the age of 65, whose thinning skin impairs the production of D. Individuals with darker skin can also be at risk, because melanin, the pigment that produces skin color, acts as a natural sunscreen. And some people, such as nursing-home residents, just don’t get outdoors. Americans in these groups may need a vitamin D supplement every day, or a daily dose from November through March (especially those living in the northern U.S., where winters are more severe).

Obesity can also lead to vitamin D deficiency (fat cells trap D and won’t let it go), as can medications (drugs like Dilantin for seizures interfere with the vitamin’s metabolism) and gut conditions like gastric bypass surgery, inflammatory bowel disease or laxative overuse (by impairing D’s absorption). Those with low D may experience fatigue, bone pain, muscle weakness or depression, though many suffer no symptoms. Left untreated, this can lead to osteoporosis (low bone mass), osteomalacia (bone softening) or myopathy (muscle disease).

Whether it’s to compensate for poor eating habits or too much time spent indoors, or just for nutritional peace of mind, Americans spend over $50 billion on vitamins annually. With the exception of daily multiple vitamins, more vitamin D pills are purchased than any other nutritional supplement. Even though experts recommend only high-risk individuals should take a modest dose of 600 international units (IUs) a day, millions take up to 5,000 IUs. This overdosing can have dangerous consequences: confusion, poor balance, nausea and thirst. Each year there are 4,500 cases of D toxicity from excessive supplementation across the U.S.,
sometimes leading to hospitalization or death.

Many scientists agree the simplest way to get enough vitamin D is what most Americans already do: Get a little sunblock-free sunshine daily in the spring and summer. Light-skinned people need 10 to 15 minutes per day; for those with dark skin, it’s 20 to 30. Because extensive UV exposure or sunburn can lead to skin cancer, it’s best to apply 30 SPF sunscreen after that. Discuss the best regimen for you with your medical provider.

Vitamin D-rich foods can also help. Fatty fish like salmon is the best source, followed by mushrooms, soy and egg yolks. Other options include D-fortified products like milk, orange juice and dry cereal.

Contact your medical provider for a baseline blood test if you’re at risk for D deficiency; the results will help determine if you need a part time or year-round dose. An OTC supplement of 600 to 800 IUs is the usual recommendation.

Choose vitamin D3 over D2—it’s better absorbed—and research the manufacturer. (Solgar and Life Extensions are reliable brands.) D supplements are best taken with food; wait at least an hour before taking any other medication. Repeat a vitamin D blood test after four to six months to make sure your over-the-counter dose is adequate.

And remember, springtime isn’t that far away.

Mary Jenkins recently retired after nearly 40 years as a family practice physician in New York  state.