Why we need it: This fat-soluble vitamin aids in the absorption of calcium and regulates blood levels of calcium and phosphorus, which is key to maintaining strong bones and teeth. Vitamin D deficiency is the leading cause of rickets, a softening of bones usually seen in children that can lead to bone fractures and deformities such as bowlegs. The nutrient is also important for keeping the immune system strong.
Best foods for it: Eggs, liver, oily fish such as salmon, fortified milk and dairy products, and fortified cereals and orange juice.
Do you need a supplement? Possibly. “The latest research shows that people are not getting enough vitamin D because few foods in nature contain it,” says Dr. Gerbstadt. Breast milk also doesn’t provide enough of the nutrient, so the American Academy of Pediatrics recommends giving infants who are exclusively or partially breastfed 400 IU of vitamin D supplements daily. Once they are weaned and drinking at least a quart of vitamin D-fortified milk or formula each day, they may no longer need supplements.
The bottom line: “Without including fortified foods, you can’t get enough vitamin D in your diet,” says Dr. Gerbstadt. And don’t count on the sun’s ultraviolet rays, which trigger vitamin D synthesis, to meet your needs. “Whenever you’re out in the sun you should be wearing sunscreen, which blocks this process,” she says. Instead, consider talking to your doctor about taking a vitamin D supplement or a daily multivitamin containing D.