Decoding the Science of Vitamin D

Fact or Fiction?

We all know vitamin D is important for strengthening bones, developing muscles, fighting infection, and improving heart and lung health. But, do you know how it’s made or if you’re getting enough of it? Read on to learn about how to separate fact from fiction with this important nutrient.

You can get all the vitamin D you need from a healthy diet:


Unlike many of the vitamins and minerals our bodies need to operate effectively, vitamin D is not found in healthy classics like kale or quinoa. In fact, there are only a handful of foods that have adequate amounts of this important nutrient. “The average American diet is not as rich in vitamin D as it is in other vitamins, making it challenging to obtain an adequate supply from your diet,” says Pamela Kelle, registered dietitian and licensed nutritionist. “Most of the foods that do supply vitamin D are not favored by many people.” Cod liver oil is one of the best sources of vitamin D, with more than 200% of the required daily intake in just one tablespoon. Wild-caught salmon and mackerel are not far behind, both containing about half of the recommended daily intake. Calf liver and egg yolk are also relatively high in vitamin D, along with canned tuna and sardines, and shitake mushrooms.

vitamin d capsules

Though not naturally found in milk, many manufactures add vitamin D to milk.

If cod liver oil-dipped mackerel, with a side of fortified milk, isn’t on your menu tonight, don’t worry. Other options exist for getting your daily dose of vitamin D.

Your body can produce vitamin D when skin is exposed to the sun:


Unlimited access to vitamin D is literally outside your front door. There are two different forms of vitamin D: D2, which is produced by plants and can be consumed in some foods, and D3, which is created by our skin when it is exposed to light. The sun’s ultraviolet B rays hit the skin and convert cholesterol into an active form of vitamin D.

We all know the risks associated with too much sun, but getting your daily intake of D3 doesn’t require much time outside. “Vitamin D absorption is affected by a number of factors including your level of skin pigmentation, the time of day you are outside, and pollutants in the air,” Kelle says. It should take about half the time it takes for your skin to start to burn to absorb enough sunlight to make your recommended amount of vitamin D. This may be 15 minutes if you have fair skin and freckles or more than an hour if you have dark skin.

Only about 10% of vitamin D comes from what we eat.

Vitamin D is a considered a hormone:


Vitamin D’s name is misleading. Also called calcitriol, this nutrient is a steroid hormone that regulates the body’s levels of calcium and phosphorus, aids in cell growth, improves immune function, and reduces inflammation. Unlike other vitamins that are simply consumed by the body, Vitamin D3 is generated in the skin of humans and animals. According to Audrey Picklesimer, a registered dietitian and licensed nutritionist with CHI Memorial, “Vitamin D is made by our bodies as a result of skin exposure to sunlight. During this exposure, the body produces what is called cholecalciferol, and, in turn, that is converted to what we call “activated” vitamin D. This is when vitamin D is ready to do its jobs, like maintaining calcium in bones, controling the blood and gastrointestinal tract, and sending appropriate signals for our cells to communicate adequately.”

Most Americans have deficient levels of vitamin D:


As a whole population, the  U.S. does a decent job of maintaining enough vitamin D in their blood, but deficiency of this critical nutrient is a serious problem for many individuals, and certain population groups are at higher risk. A 2011 study from Slippery Rock University of Pennsylvania found that more than 41% of U.S. adults are deficient in Vitamin D. The number goes up to more than 69% in the Hispanic-American population and exceeds 82% among African-Americans. The elderly population is also at higher risk of vitamin D deficiency, primarily due to decreased time outside.

According to the Institute of Medicine, the recommended daily amount of vitamin D is 600 international units (IUs) for individuals under age 70 and 800 IUs for those 70 and up. Individuals who have low levels of the vitamin can safely consume or absorb between 2,000 to 4,000 units per day.

I’d know if I had a vitamin D deficiency:


Before the 1920s when dairy companies started fortifying their milk, the best indicator of a vitamin D deficiency was rickets, a childhood bone disorder that has been nearly eradicated in the developed world.

According to Dr. Curtis Cary, an internal medicine physician at Erlanger, “These days, vitamin D deficiency varies greatly, with most deficient people showing no symptoms at all.” And if symptoms do present, they can be subtle and difficult to pinpoint. They include frequent sickness and infections, fatigue, bone and back pain, depression, slow healing wounds, bone loss, hair loss, and muscle pain. “Symptoms of vitamin D deficiency are not necessarily easy to recognize. Vitamin D deficiency is associated with low bone mass & osteoporosis.

pills in yogurt cups

Some people may experience bone pain or muscle weakness, but the best way to  detect deficiency is by a blood test performed by a doctor,” says Picklesimer. Your risk for vitamin D deficiency increases if you are overweight, elderly, have dark skin, live in a cold climate, or spend most of your time indoors. If you suspect your vitamin D levels are low, the only way to find out for sure is to get a blood test.

There is ongoing debate about what levels of vitamin D are considered healthy and sufficient. Deciphering your blood level number and whether you are vitamin D deficient is a task best left to your doctor.

It is possible to take too much vitamin D:


If you are experiencing some symptoms of vitamin D deficiency, you may be tempted to skip the blood test and buy a supplement at your local drug store. Unfortunately, vitamin D toxicity is a real consequence of over-supplementation that causes a build-up of calcium in the blood. “It is not clear at what level vitamin D becomes toxic, but it is usually limited to individuals consuming extraordinarily high levels of supplements,” says Dr. Cary. While rare, symptoms of this condition include poor appetite, nausea, vomiting, weakness, frequent urination, and kidney problems. “Because vitamin D is a fat soluble vitamin, it is not as readily eliminated by our bodies as water-soluble vitamins. According to the Institute of Medicine, the tolerable upper limit is 4,000 International Units per day which meets the needs for most healthy people,” says Picklesimer.

If you suspect you are vitamin D deficient, get a simple blood test to avoid this harmful condition. You and your doctor can use the results to develop a safe, effective plan to get your vitamin D levels in check.

Picture of Pamela Kelle

Pamela Kelle

Registered Dietitian, Licensed Nutritionalist, and Certified Eating Disorder Registered Dietician

Picture of Audrey Picklesimer

Audrey Picklesimer

Registered Dietitian, Licensed Nutritionist, Certified Diabetes Educator, CHI Memorial Diabetes and Nutrition Center

Picture of Dr. Curtis Cary

Dr. Curtis Cary

Internal and Pediatric Medicine Physician, Erlanger Community Health Centers at Dodson Avenue and Southside

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