If you live in Minnesota it's likely you've wondered whether you're getting enough vitamin D, especially in winter when getting outside can be difficult.
A new study may provide some relief.
The study at the Loyola University Chicago Stritch School of Medicine looked at vitamin D data from a national sample of 2,877 children and adolescents ages six to 18 who participated in the National Health and Nutrition Examination Survey.
Researchers found that fewer children are at risk for vitamin D deficiency than previously thought. Just over ten percent of children ages six to 18 were at risk of having vitamin D levels that are too low.
Overweight, female and non-white children, and teens between the ages of 14 and 18 were more likely to be at risk of vitamin D deficiency.
Overall, the study found more than five million children in the U.S. are at risk of inadequate or deficient vitamin D levels.
That number is far lower than estimates from a 2009 study published in the journal Pediatrics, which defined sufficient vitamin D levels as greater than 30 ng/mL.
The 2009 study found that an estimated 70 percent of people ages 1 to 21 had deficient or insufficient vitamin D levels. Previous guidelines from the Institute of Medicine required vitamin D supplements for millions of children in this range. New institute guidelines don't require children in this range to take vitamin D supplements.
Still, vitamin D deficiency remains a major worldwide concern. An estimated 1 billion people are thought to have inadequate levels of vitamin D in their blood.
What is vitamin D?
The term "vitamin D" refers to several different forms of this vitamin.
Two forms are important in humans: vitamin D2, which is made by plants, and vitamin D3, which is made by human skin when exposed to sunlight.
The major role of the vitamin is to maintain normal blood levels of calcium and phosphorus. Vitamin D also helps the body absorb calcium, which forms and maintains strong bones. And vitamin D can also help prevent a long list of chronic diseases, including osteoporosis, high blood pressure, cancer, and other diseases.
But scientists have debated just how much vitamin D people need each day.
The Institute of Medicine currently calls for an intake of vitamin D at 5 micrograms (200 IU) for people up to age 50, 10 micrograms (400 IU) for people between the ages of 51 and 70, and 15 micrograms (600 IU) after age 70.
Harvard researchers say optimal intakes are much higher, though, with at least 25 to 50 micrograms (1,000 to 2,000 IU) recommended for those over age two.
In general, research has found that the risk for low vitamin D levels is higher for people with darker skin and people living in northern latitudes - like Minnesota. The same is true for people who are overweight or obese.
And correctly applying sunscreen limits the body’s ability to absorb vitamin D by as much as 90 percent.
To increase vitamin D levels, the Mayo Clinic recommends getting outside each day.
Exposure to sunlight for as little as 10 minutes a day is thought to prevent vitamin D deficiency, and can help make up for the lack of vitamin D found in food.
Foods rich in vitamin D include: Eggs, fortified milk, dairy products, breakfast cereals and fatty fish such as salmon and tuna.