If you’re feeling down in the winter, spending life indoors or under a coat, then you may be needing an extra boost of vitamin D.

Dr. Kathryn Glass, a family medicine physician at Mercy Primary Care at Lourdes hospital, said vitamin D is a substance the body needs to allow bones to absorb calcium. Muscles also use vitamin D to absorb magnesium. Bones need calcium for strength and muscles depend on magnesium to expand and contract. Pediatric patients with a deficiency of the vitamin may find themselves at risk for the bone disease rickets. The body produces vitamin D through exposure to sunlight. Heavy clothes, spending time indoors and sunscreen may inhibit vitamin D production.

“We also believe vitamin D deficiencies play a role in fibromyalgia and some cancers. It’s found through the body in places like breast tissue and the colon. Over time, I think we will find it is important in more and more parts of the body,” Glass said.

Glass said the current recommended daily allowance the U.S. Food and Drug Administration recognizes, 400 international units, is widely considered insufficient. She recommends between 800 and 1,000 iu per day as an appropriate amount.

“Vitamin D is a fat soluble vitamin, so you don’t want to take too much too often without consulting a doctor,” Glass said. “It works in the body like a bank. You can put a lot away with one big dose per month, then take a little out at a time, or you can put a little in and take a little out all the time.”

Sandra Farthing, a nutritionist at Lourdes, said many milk and dairy products are fortified with vitamin D. Some milk substitutes are also fortified.

“The best source is the sun, and 10 minutes of sun is about all you need,” Farthing said. “A tanning bed will not give you any vitamin D.”

Farthing said people with both fair and dark complexions have different needs for sunshine and should consult a doctor to monitor vitamin D levels.

Breastfed babies, those at risk for osteoporosis — including menopausal women— people who avoid milk and those on regular doses of corticosteroids are also at risk of vitamin D deficiency.

“Vitamin D may even play a role in patients’ moods. I’ve seen people who say they feel better with higher levels of vitamin D,” Glass said.