'' Vitamin D is often called the `` sunshine vitamin '' because the human body makes it only when exposed to sunlight -- although it only takes 10 to 15 minutes a day to make an adequate amount . Vitamin D , which helps the bones better absorb calcium , is also added to multivitamins and milk . In Melamed 's study , the researchers looked at the vitamin D levels of more than 6,000 people ages 1 to 21 . They checked for vitamin-D deficiency , which is defined as less than 15 nanograms per milliliter of blood -LRB- ng/mL -RRB- , and vitamin-D insufficiency , which is defined as 15 to 29 ng/mL . Overall , 7.6 million , or 9 percent , of U.S. children were vitamin-D deficient , and another 50.8 million , or 61 percent , had insufficient levels of this important vitamin in their blood . Children with low levels of vitamin D were more likely to have high blood pressure and lower levels of high-density lipoprotein , also known as good cholesterol -- two factors that are considered major risk factors for heart disease later in life . Health.com : How cholesterol affects
A whopping 70 percent of American kids are n't getting enough vitamin D , and such youngsters tend to have higher blood pressure and lower levels of good cholesterol than their peers , according to two new studies published this week in the journal Pediatrics . Low vitamin D levels also may increase a child 's risk of developing heart disease later in life , experts say . People who drank milk less than once a week were among those most at risk for vitamin-D deficiency , a study found . `` We were astounded at how common it was , '' says study author Dr. Michal Melamed , an assistant professor of medicine , epidemiology , and population health at the Albert Einstein College of Medicine , in the Bronx , New York . `` There is a lot of data that suggests adults with low vitamin-D levels are at risk for diabetes , high blood pressure , cardiovascular disease , and a lot of cancers , and if kids start out with low levels and never increase them , they may be putting themselves at risk for developing all of these diseases at a much earlier age .