Over six million kids in the US lack sufficient levels of Vitamin D, according to a Harvard Medical School study.

Early indications of vitamin D deficiency are profuse sweating, restlessness, and irritability. Of course, these are also indications of parenting. But seriously, long term deficiency can increase risk of heart disease, rickets, and weak bones.

After studying a bit, we learned that Vitamin D is stored mainly in the liver. It must be processed (metabolized) by the liver and kidneys into an active form called calcitriol This active form promotes absorption of calcium and phosphorus from the intestine. Calcium and phosphorus, which are minerals, are incorporated into bones to make them strong and dense (a process called mineralization). So, the vitamin is necessary for the formation, growth, and repair of bones. Good for us. Good for our kids.

Vitamin D also enhances immune function and improves muscle strength.

Requirements for vitamin D increase as people age, but the recommended amount for our kids was updated in 2008:

“The American Academy of Pediatrics (AAP) updated their guidelines in 2008 for vitamin D intake in infants, children, and teens. Their latest guidelines increased the recommended minimum daily intake from 200 IUs to 400 IUs per day of vitamin D for all infants, children, and adolescents beginning in the first few days of life.”

For the study, reported in the November issue of Pediatrics, Dr. Mansbach and colleagues collected data on about 5,000 children under age 12 who participated in the 2001-2006 National Health and Nutrition Examination Survey.

Based on the data, the researchers found that 6.3 million U.S. children — almost one in 5 — were at less than the recommended 50 nmol/L level of vitamin D.

How to Boost Vitamin D

Sun exposure is best for obtaining vitamin D, because the skin manufactures the nutrient upon exposure to sunlight. However, during the winter, UVB rays in Northern states can be insufficient for vitamin D production, experts say, and sunscreen use in summer can also reduce the skin’s ability to produce vitamin D. Only a few foods contain vitamin D naturally, namely fatty fish such as salmon, egg yolks, some cheese and some meats, including liver. Milk and some cereals are fortified with vitamin D.

Mansbach recommends vitamin D supplements, especially for those living in areas where the sun is scarce in the winter. Here again, the authors say more research is needed to determine the appropriate dosage.

“Summer sunlight exposure is the major source of vitamin D for most people,” he said. “But [too much] sun exposure can cause sunburns and eventually skin cancer. Until more research is performed, we think the safest bet is to take vitamin D supplements,” he said.

Some experts argue that more foods, such as pasta and bread, should be fortified with vitamin D.

What’s the take away? Outdoor time has more value than just fresh air and physical exercise. It can help maintain a healthy balance of vitamin D. If you live in an area without much sun, a healthy diet will help,and vitamin supplements that include vitamin D can make a difference in the health of your child.

For more information on vitamin D, check out the Nemours Foundation.