Have a D-ficiency? Here are facts on vitamin D

A campaign last year encouraging people to soak up some sun or slip into a tanning bed to prevent a vitamin D deficiency created all kinds of confusion for a generation used to slathering on sunscreen.
On one hand, skipping a sunscreen and getting burned could put them at risk for skin cancer. On the other, using a sun block could mean they would not be getting enough vitamin D.
To shed some light on the vitamin debate, here are the facts, along with some expert advice on whether to rely on sunshine or a supplement for a daily dose of D.
Vitamin D basics
Vitamin D is fat-soluble. People get most of their vitamin D from exposure to sunlight and a few foods. The vitamin promotes the absorption of calcium and helps strengthen bones. There’s growing evidence that many people — by some estimates 60 percent or more — don’t get enough vitamin D.
Supplements vs. sunlight
A little exposure to sunlight — 10 to 15 minutes a week — is enough to supply children and young adults with all the vitamin D they need.
The trick is to not overdo it.
It’s one thing to let children play outdoors without a sunscreen for 15 minutes and another to let them go all day without protection, said Jo Ann Carson, professor of clinical nutrition at UT Southwestern Medical Center.
Parents who tend to forget to slather sunscreen on the kids would be better off giving them a vitamin D supplement rather than risk them getting too much sun exposure, she said.
Besides, going out much longer in the sun than the recommended 15 minutes has no additional benefits because the body won’t absorb it.
The rules change as people age. After age 50, the skin loses its ability to absorb vitamin D from sunlight. By 70, forget about the sun and take a supplement.
Foods rich in vitamin D
Salmon tops the list of foods rich in vitamin D, followed by low-fat milk. Margarine, eggs, beef liver and Swiss cheese also contain small amounts of the vitamin, according to the National Institutes of Health.
How much is enough?
For those 50 and younger, 200 International Units (IU) per day, the equivalent of two glasses of milk, is adequate. For those 51-70, the recommendation is 400 IU, and over 70 it’s 600 IU, according to the National Institutes of Health. But some researchers suggest 1,000 to 5,000 IU a day is safe.
Not enough D
A vitamin D deficiency can lead to rickets and weak muscles. In recent years, several studies have linked a lack of vitamin D with cardiovascular disease, high blood pressure, diabetes and high triglycerides. There’s also evidence that a lack of D is linked to certain cancers and immune dysfunction.
One study published in the American Journal of Clinical Nutrition found that taking 1,000 IU of vitamin D daily reduced the risk of getting cancer.
Too much D
Supplements with calcium and vitamin D can increase the risk of kidney stones. More than 2,000 IU is not recommended. Studies have indicated that doses of up to 10,000 IU per day are not toxic but are not recommended. Taking too much can cause nausea, poor appetite, weakness, weight loss and confusion.
Who’s at risk for a vitamin D deficiency?
Breastfed infant — Human milk does not provide adequate vitamin D.
Older adults — Their skin has difficulty synthesizing vitamin D
People with limited exposure — Those who live in northern latitudes and women who wear long robes and head coverings for religious reasons don’t get enough exposure to sunlight.
People with darker skin — They have greater amounts of melanin, which reduces the skin’s ability to produce vitamin D from sunlight.
Obese people — Their fat cells extract vitamin D from blood and hoard it.
Sources: Harvard Public Health Review, The National Institutes of Health, Food and Drug Administration, Vitamin D Council, NetWellness