Factors that might affect your vitamin D levels
Your vitamin D levels reflect many factors. For example:
Where you live. If you live in the northern states (latitudes north of 37°), you are at higher risk for a vitamin D deficiency because your skin may not be able to produce any vitamin D from sun exposure during the winter months.
Your age.
Your skin's ability to produce vitamin D drops with age. If you're over age 65, you generate only one-fourth as much vitamin D as you did in your 20s.
Your skin color.
People with darker skin typically have lower levels of vitamin D than lighter-skinned individuals. African Americans have, on average, about half as much vitamin D in their blood compared with white Americans.
Your weight.
If you have a body mass index above 30, you may have low blood levels of vitamin D. Vitamin D is stored in fat, so in people with obesity, less of the vitamin circulates in the blood, where it's available for use by the body.
The foods you eat.
Very few foods naturally contain vitamin D. The U.S. government started a vitamin D milk fortification program in the 1930s to combat rickets, a bone-weakening disease caused by vitamin D deficiency, which was a major public health problem at the time. Breakfast cereals and some types of orange juice may also be fortified, but this varies by brand. So, the amount of vitamin D you get from food depends on the food you eat and how much milk you drink.
Certain health conditions.
People with conditions such as inflammatory bowel disease, liver disease, or cystic fibrosis, among others, may have trouble absorbing vitamin D, which can lead to deficiencies.
