13. Do You Need a Vitamin D?

People who are at risk for a vitamin D deficiency and so may need supplements include:

• Infants who are breastfed. Breast milk doesn't contain enough vitamin D to meet a baby's needs, and infants also don't usually get enough exposure to sunlight to make enough vitamin D on their own. The American Academy of Pediatrics recommends that breastfed infants receive a vitamin D supplement of 400 IU per day.
• Individuals who have limited exposure to the sun. People who are homebound or who don't often get outside are probably not making sufficient vitamin D.
• Vegetarians and vegans. People who don't eat fish, eggs, or milk may have a harder time getting vitamin D from the foods they eat.
• People who are lactose intolerant or have a milk allergy. Milk is fortified with enough vitamin D to be a good source of it, but if you need to drink an alternative to milk, such as soymilk, make sure it's fortified, too.
• Adults over age 50. People over age 50 need extra vitamin D because, for one thing, our skin becomes less able to make vitamin D as we age. For another, our kidneys lose some of their ability to convert vitamin D into the particular type our bodies can use.
• People with dark skin. The more melanin in the skin, the less vitamin D the skin can produce.
• People who are obese. Vitamin D is a fat-soluble vitamin and so can be stored in fatty tissue. The bodies of people who have excess fat, however, may store up too much of the vitamin and not be able to release it into circulation when it's needed.
• Those who use sunscreen. Don't, however, limit your sunscreen use for fear of not making enough vitamin D. Some vitamin D is usually still made, even when we wear sunscreen because most people don't cover every inch of skin, or they don't apply as much as they need, or they don't reapply it as often as needed.
• Individuals who have liver disease or whose bodies don't absorb fat properly. Because vitamin D is a fat-soluble vitamin, people whose bodies either can't tolerate fat or can't soak up enough fat may not be able to absorb the levels of vitamin D they need.

Vitamin D deficiency can cause weakened bones and lead to osteoporosis. Recent research has now linked a vitamin D deficiency to breast-cancer progression. Think about your diet and your average daily time in the sun, and then talk with your doctor about whether you might need a supplement.