On Your Health

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Why You Need Vitamin D

Vitamins and nutrients are essential to help your body fight illness and stay in good health. Unlike most vitamins found in nutrient-rich foods, getting the proper amount of vitamin D is a little trickier.

Vitamin D, also called the sunshine vitamin, is unique because your body can produce it on its own when your skin is exposed to sunlight. The problem is, the amount of vitamin D your body produces is limited by many factors, making it difficult to get the amount of vitamin D your body needs from the sun.

We’ve explored why vitamin D is necessary for maintaining your health, how best to get it, and how to know if you’re getting enough.

Vitamin D deficiency

According to a recent study, more than 41 percent of adults in the U.S. were vitamin D deficient. Those most at risk are older adults, those with darker skin tones, those with kidney or liver disease and those who do not get enough direct sun exposure. A lack of vitamin D can not only affect your bones but other parts of your body, too.

In children, vitamin D deficiency can lead to rickets, a condition that causes the bones to become too soft and unable to support weight. In adults, osteomalacia, a disease that causes bones to weaken and become more likely to break, can result from a lack of vitamin D.

If left untreated, both rickets and osteomalacia can cause brittle bones, bone pain, muscle pain and general weakness.

For older adults, long-term vitamin D deficiency can lead to osteoporosis, a condition that causes a reduction in bone density with an increased risk of bone fractures. Besides not getting enough sun, there are several other things that can cause vitamin D deficiency.

Kidney and liver disease – Both reduce the production of certain enzymes needed to change vitamin D into an activated form that can be used by the body.

Cystic fibrosis, Crohn’s disease and celiac disease — All of these inhibit the intestines from absorbing vitamin D.

Obesity – Having a body mass index greater than 30 can cause vitamin D to become trapped inside excess fat rather than being released into the bloodstream.

Aging – Lessens the skin’s ability to absorb vitamin D.

Darker skin tones – Dark-colored skin is less able to make vitamin D.

Human breast milk – Breast milk contains very little vitamin D, making it easy for infants who are exclusively breastfed to become deficient.

Mobility – Those who are homebound or rarely go outside struggle to produce vitamin D due to lack of sun exposure.

Medications – Laxatives, steroids (like prednisone), cholesterol-lowering drugs (like cholestyramine and colestipol), anti-seizure medications (like phenobarbital and phenytoin), a tuberculosis drug (rifampin) and a weight-loss drug (orlistat) are all known to reduce vitamin D levels.

Why is vitamin D beneficial?

Vitamin D aids your body in the absorption of calcium — the nutrient responsible for maintaining healthy, strong bones and teeth. Without vitamin D, your body can only absorb 10 to 15 percent of the calcium you consume. This is why milk, which is high in calcium, is often enriched with extra vitamin D. Vitamin D also helps your body absorb other essential nutrients like iron, magnesium, zinc and phosphorus.

This super vitamin has been proven to keep your immune system functioning normally, help prevent certain cancers and improve cognitive function. By supplementing naturally made vitamin D with oral supplements or foods rich in vitamin D, this vitamin can also help treat inherited disorders resulting from an inability to absorb vitamin D.

Sources of vitamin D

In order to get all of the health benefits, it’s important to make sure you’re getting the appropriate amount of vitamin D. The three main sources are food, sunlight and supplements.


Very few foods are naturally high in vitamin D, so most Americans get vitamin D from fortified foods. Common foods that are natural sources of vitamin D include fatty fish (salmon, tuna, mackerel, etc.), beef liver, cheese, egg yolks and mushrooms. Milk, breakfast cereals, orange juice, yogurt, margarine and soy beverages are commonly fortified with vitamin D to make it easier for consumers to get appropriate amounts. Keep in mind that most foods do not meet the daily recommended levels of vitamin D on their own.


Most people meet at least a portion of their recommended amount of vitamin D from sunlight. Unfortunately, many factors can limit the amount of vitamin D your skin is able to produce, including the time of day, season, the latitude at which you live and the pigmentation of your skin. For example, those who live in the northern U.S. make less vitamin D than those in the south, especially during the winter months when the sun is lower in the sky for long periods of time.

Overcast skies, shade and a darker skin color also limit the amount of sunlight your skin is able to absorb, thus limiting the amount of vitamin D produced. Even being exposed to sunlight through a window while indoors inhibits your skin from producing vitamin D.

Despite the importance of sunlight in vitamin D production, you still need to limit your direct exposure to the sun in order to lower your risk of developing skin cancer. You only need to expose your face, arms, legs or back to the sun for five to 15 minutes, a couple of times a week, to get an adequate amount of vitamin D.  


For those who can’t get enough vitamin D from their diet or sunshine, vitamin D supplements are available. Older adults who don’t usually get regular exposure to sunlight and have trouble absorbing vitamin D can benefit from supplements to help improve bone health. Supplements are also helpful for those with darker skin tones as well as those who have been identified as being vitamin D deficient by their doctor.  

How much vitamin D do you really need?

In recent years, researchers have discovered that Americans need more vitamin D than previously thought. The Food and Nutrition Board of The National Academies of Sciences, Engineering and Medicine provides recommendations on the amount of vitamin D people of different age groups and life stages should be consuming on a daily basis. Since the absorption of vitamin D through the skin varies so greatly between individuals, these recommendations assume people are getting minimal sun exposure.

Recommendations are given in international units (IU), an internationally accepted amount of a vitamin, and micrograms (mcg). On food and supplement labels, the amount of vitamin D present may be given in either international units or micrograms.

The chart below provides the daily recommended amount by life stage. Your doctor can also recommend the appropriate amount of vitamin D for your body and health.

Vitamin D intake chart

Overdosing on vitamin D

In the same way that too little vitamin D can be harmful to your health, consuming too much vitamin D can also have negative consequences. While overdosing on vitamin D, also called vitamin D toxicity, is rare, it can happen. Vitamin D toxicity occurs when amounts in the bloodstream become too high and can cause symptoms like nausea, vomiting, poor appetite, increased thirst, constipation, weakness, weight loss, confusion and disorientation, heart rhythm problems, kidney damage and possibly pancreatic cancer.

Vitamin D overdose is most often caused by overuse of supplements. Excessive exposure to sunlight cannot cause vitamin D toxicity because the body limits the amount of the vitamin that it naturally produces. The recommended upper limits for vitamin D consumption are listed below.

  • Birth to 12 months – 1,000 to 1,500 IU
  • Children 1 to 8 years old – 2,500 to 3,000 IU
  • Children older than 9, teens, adults and pregnant and breastfeeding women – 4,000 IU

Do not take more than the recommended amount without first discussing it with your doctor. Depending on your health, your doctor may recommend higher doses of vitamin D, but your doctor should check your blood levels regularly and adjust doses accordingly.