Vitamin D: Should You Supplement?

Photo by Patrick Tomasso @iampatrickt

Photo by Patrick Tomasso @iampatrickt


As the temperature drops and the daylight hours shorten, you may find yourself with less time and inclination to be outside. One essential benefit to being outside is sun exposure and subsequent vitamin D synthesis. However, depending on where you live, you may not get enough exposure to the sun during the fall and winter months to make adequate vitamin D.


Vitamin D deficiency affects multiple body systems including skeletal, muscular and nervous. Insufficient vitamin D can lead to bone tenderness and demineralization, muscle weakness, twitching, and pain. It may even affect your memory!

Your body makes vitamin D through processes in three of your organs: your skin, liver and kidneys. The process starts in your skin. A substance in your skin absorbs UV light from the sun and converts it to something called vitamin D3.  Vitamin D3 is also the form found in food or supplement sources of vitamin D. Making vitamin D3 active involves first your liver then your kidneys.

There are many factors that affect how you absorb UV light from the sun to make vitamin D.



Melanin is responsible for the pigment in your skin. The more pigmentation in your skin, the harder it is for your melanocytes (melanin cells) to absorb sunlight to photosynthesize vitamin D. Lighter skinned individuals need 10-15 minutes of sun exposure to your face, neck, hands and arms for adequate vitamin D production. Studies show that individuals with darker skin pigmentation make less serum 25(OH)D from the same amount of sun exposure. Therefore, more sun exposure may be necessary for individuals with darker skin to meet the same serum vitamin D levels as those with lighter skin.



Sunscreen protects against sun damage and the very scary prospect of skin cancer. However, sunscreen also blocks sunlight from penetrating your skin to make vitamin D by absorbing the ultraviolet light. Clothing also serves this same protective function. While good for protecting against skin cancer, both reduce your body’s ability to make vitamin D.



Once fall hits and you live above the 30th parallel north, your body cannot synthesize vitamin D from the sun. In the U.S., that means anywhere north of about New Orleans or Houston. From October to May, UV rays become more oblique due to the angle of the Earth to the sun. Therefore, regardless of the time you spend outside in the sun, you simply cannot synthesize enough vitamin D from the sun during these months.


From June to September or if you live in a sunny place below 30˚N, the National Institute of Health (NIH) recommends safe exposure times to ensure adequate vitamin D synthesis may be in the range of 5-30 minutes of sun exposure from 10 am - 3 pm twice a week to your face, neck, arms, and hands to maintain healthy vitamin D levels.


How to know you’re getting enough

Get tested! There are a variety of vitamin D tests that your primary physician can order for you. A good test is the serum 25(OH)D test. Levels of vitamin D adequacy range from 20ng/ml to between 40-80 ng/ml depending on which scientific organization’s recommendations you follow. The Institute of Medicine is most conservative at 20ng/ml and recommends a daily vitamin D supplement of 600IU. The Endocrine Society recommends 2,000IU a day while the Vitamin D Council recommends 5,000IU to achieve their suggested optimal vitamin D serum blood levels. When looking at optimal vitamin D levels of people who live in sunny places year round, a daily vitamin D intake of 2,000IU may be most appropriate.  

The serum 25(OH)D test is a biomarker for the vitamin D your body has made from the sun, food and supplements but it doesn’t necessarily tell you how the levels relate to the health outcomes associated with Vitamin D. In fact, some studies show that African Americans having low serum 25(OH)D levels actually have reduced rates of fracture and osteoporosis compared to Caucasians.  Therefore, the test is not all encompassing and depending on your age, skin color and geography, your doctor will be the best able to help you interpret your test results and determine the need to supplement.


When to supplement

There are two routes to take to ensure you have adequate vitamin D stores when unable to synthesize sufficiently from the sun: supplementation and food sources. This is especially helpful when you use sunscreen and protective clothing while in the sun, have darker pigmented skin and limit sun exposure.

While there are not a lot of natural food sources of vitamin D, fatty fish, egg yolk, and beef liver are some foods that do contain vitamin D. More common are vitamin D-fortified foods which include cow’s milk, orange juice, and ready-to-eat cereal.


What you can do

1)    Check your vitamin D levels to get a baseline.

2)    If you and your doctor decide you should supplement, take your supplement with your largest meal. Studies show that doing so increases vitamin D blood levels by 50%.

3)    Want more info? Check out Nutrition videos for more information behind the daily 2,000IU vitamin D recommendation.