Vitamin D is called a vitamin but it behaves more like a hormone. One of its most important functions is to boost calcium absorption from your intestinal tract. This helps to keep your bones healthy, among other things. Interestingly, vitamin D also increases the absorption of other minerals from your intestinal tract including zinc, iron, magnesium, and phosphate.
What’s the best source of vitamin D? Sunlight converts a chemical on your skin to a vitamin D precursor. Once this precursor is made it’s processed by your liver and kidneys to make active vitamin D.
Despite the ability of your body to make active vitamin D, low vitamin D levels are common. Research shows the number of people who are deficient or marginally low in vitamin D ranges from 30% to 60%, depending upon the source you look at. That’s concerning since low vitamin D levels have been linked with health problems like osteoporosis and autoimmune diseases like multiple sclerosis. In fact, tissues throughout your body have receptors for vitamin D, showing its far-reaching effects. Plus, there’s preliminary evidence that vitamin D may lower the risk of some chronic diseases but this is still unproven.
Having a low vitamin D level can even affect your exercise performance. Not only is vitamin D deficiency linked with muscle weakness and fatigue, but there’s also some evidence that even marginally low levels of vitamin D negatively impact athletic performance. One study showed exercise performance peaks when vitamin D levels are highest and decline as vitamin D levels drop. Some research shows a direct correlation between vitamin D levels and size and quantity of fast-twitch muscle fibers, the muscle fibers best adapted for strength and power moves.
Having normal blood levels of vitamin D is important for overall health and for athletic performance. Are you at risk for vitamin D deficiency? Here are six signs you’re at higher risk:
Risk For Vitamin D Deficiency: You Don’t Consume Meat or Dairy Foods
Research shows people that eat a vegan diet are more likely to have a low vitamin D level.
That’s because dairy milk is one of the best dietary sources of vitamin D. Eggs also contain a modest amount of vitamin D as long as you eat the yolk. Some foods are fortified with vitamin D including yogurt, cereal, and orange juice.
If you get enough exposure to direct sunlight, you don’t have to depend on dietary sources of vitamin D but it can be challenging if you live in areas with little direct sunlight. Some milk substitutes suitable for vegans like almond milk and soy milk are fortified with vitamin D. This can help you get more dietary vitamin D if you eat a vegan diet.
Risk For Vitamin D Deficiency: You Have Darker Skin
If you have a lot of pigment in your skin, your skin can’t make as much vitamin D precursor. This means you need more exposure to sunlight to meet your vitamin D requirements. How much sun exposure does the average person need to maintain an adequate vitamin D level? Between 15 and 30 minutes three times a week is adequate but you need more than this if you have darker skin.
Risk For Vitamin D Deficiency: You’re Over the Age of 60
Studies show vitamin D deficiency is more common in older adults and seniors than in the younger population. This is partially due to reduced sun exposure. Older people also have reduced ability to make active vitamin D from exposure to sunlight.
Risk For Vitamin D Deficiency: You Have Other Medical Problems or Are Taking Certain Medications
If you have liver, kidney or intestinal disease, especially inflammatory bowel disease, you may have lower vitamin D levels. In addition, some people have inherited conditions that affect their ability to produce active vitamin D. If you take certain medications including steroids, anti-fungal medications, and medications that prevent seizures, you may have a low vitamin D level. These medications convert active vitamin D to an inactive form.
Risk For Vitamin D Deficiency: You Stay Indoors or Slather on the Sunblock
It’s hard to make up for lack of sun exposure through diet. Assuming you aren’t deficient, you need between 600 and 800 international units of vitamin D a day and most experts believe this is too low. Considering eight ounces of milk has only 100 international units, getting enough vitamin D from dietary sources is an uphill battle.
One of the best sources of vitamin D is sockeye salmon. It has 450 international units per serving, but don’t eat it every day due to the mercury risk. It IS important to wear a sunblock to protect your skin from the sun’s damaging rays but you also need some unprotected sun exposure unless you take a vitamin D supplement. Try to strike a healthy balance.
Some areas of the world get little direct sunlight, especially during the winter months. These are the areas of the world where the risk of multiple sclerosis is highest, showing a link between vitamin D and some autoimmune diseases. If you live in one of these areas, it’s important to get more vitamin D from dietary sources and have your doctor check your vitamin D level to make sure you don’t need a supplement.
Risk For Vitamin D Deficiency: Obesity
Obesity is also a risk factor for vitamin D deficiency. Obese people are less able to access vitamin D that’s stored in their tissues.
The Bottom Line?
Vitamin D is vital for good health, athletic performance, muscle strength and, possibly, the prevention of some chronic diseases. If you fall into one of these high-risk categories, have your doctor check your vitamin D level to make sure it’s not too low.
Consultant March 2014. “Health Practitioner’s Guide to Prescribing Vitamin D and Calcium”
Medscape Family Medicine. “Prevalence and Predictors of Vitamin D Deficiency in Healthy Adults”
Med Sci Sports Exerc. 2009 May;41(5):1102-10.
Am J Clin Nutr September 2000 vol. 72 no. 3 690-693.
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