Why You Need Vitamin D

If you have had an annual physical recently, chances are you had your vitamin D level checked. And if you had your vitamin D level checked, chances are you were deficient. And if you were deficient, chances are you were given a recommendation (or even a prescription) for vitamin D.

What’s going on? Why aren’t we getting enough of this important vitamin? What has changed? Duke Primary Care family medicine doctor Matthew Payne, MD, answer questions about vitamin D deficiency.

Is vitamin D deficiency an issue for a lot of people?

Donthireddi: According to a national study, more than 40 percent of the population has a vitamin D deficiency. But at least 90 percent of my patients in my practice have a deficiency, ranging from mild to serious.

Are people getting less vitamin D than they used to?

Payne: That’s hard to say, because we haven’t always routinely checked for vitamin D levels the way we do now. But, also, sunlight is a good source of vitamin D, and people aren’t getting as much sunlight as they used to. We seem to spend more time indoors, and when we do go out, we wear sunscreen because we are more aware of the risk of skin cancer.

Why did we start routinely screening for vitamin D levels?

Donthireddi: One factor has to do with research studies, which looked at reducing pain and inflammation in cancer patients. It found that large doses of vitamin D supplements alleviated these symptoms. These studies shed more light on how vitamin D functions and its benefits.

What effect does too little vitamin D have on our body?

Payne: The number-one risk of long-term vitamin D deficiency is bone fractures and osteoporosis. This is especially true in women, because they have less bone density than men. And sufficient vitamin D is very important for kids' bone growth.

Donthireddi: Vitamin D can act on many systems in the body—particularly bone. Too little vitamin D can lead to chronic muscle and bone aches and pains, and also menstrual irregularity in women, and depression. Supplementing vitamin D in adequate quantities can also decrease high blood pressure and diabetes in those people who are at risk. Vitamin D supplements can also decrease dental cavities and risk of allergies. I’ve seen significant improvements in fatigue and irregular periods with my female patients after starting prescription vitamin D supplements.

Since sunlight is a good source of vitamin D, could the winter be to blame for lower levels?

Payne: I don’t really take into account the season. You can have vitamin D deficiency any time of the year.

Just how much sun do you need? And what are other sources of vitamin D?

Donthireddi: You can get vitamin D from food. Foods like fish and fortified juice and milk are high in vitamin D. But it is most easily available from the sun. That’s the best place to get it, and you only need 15 to 20 minutes of exposure a day. People who live in Florida typically don’t need vitamin D supplements. Sun is important!

If I do need a supplement, what should I know?

Donthireddi: The dosage is important, as you don’t want to take too much. Your doctor can determine whether you need a prescription or whether you can take an over-the-counter supplement. It’s simple. Take it for three months and you will see a difference. It's just like taking an antibiotic when you have an infection and you feel better. It’s the same with vitamin D, especially for someone who is seriously deficient. 

Ultraviolet B radiation from the sun penetrates exposed skin and converts something called 7-dehydrocholesterol in the skin to previtamin D3, which in turn becomes vitamin D. The time of day, cloud cover, skin melanin content, sunscreen, and other factors affect ultraviolet radiation exposure and the formation of vitamin D.

Source: National Institutes of Health