The Lowdown on Vitamin D: Dietary or Sun Exposure?

Vitamin D has been getting a lot of attention lately and there is good reason why. Vitamin D, a fat-soluble hormone, has many roles in the body, so it’s no surprise that vitamin D deficiency has been linked to a myriad of negative health outcomes. 

What is Vitamin D?

Vitamin D3 (also known as cholecalciferol) is a fat-soluble hormone that is acquired through ingestion of Vitamin D-rich foods or supplementation. Vitamin D can also be synthesized within the body via sunlight exposure, which in turns triggers production. Once vitamin D is acquired, it is stored in the liver or fat to be used in the future. 

Vitamin D is most known for its role to absorb calcium and contributes directly to bone health. If vitamin D levels are low, calcium cannot be adequately absorbed. This is important because calcium, in addition to special molecules called osteoblasts and osteoclasts build, shape and strengthen bone. In fact, the prefix “osteo” is Greek for bone. Therefore, when you hear of the disease osteoporosis, it in fact is derived from the phenomenon of having “porous bone.”

Vitamin D has many other roles in the body, including cell growth, immune function, neuromuscular function and genetic expression. Vitamin D receptors are all over the body, therefore vitamin D is involved in many biological processes.

What is Vitamin D Deficiency?

Serum vitamin D levels can be obtained from a simple blood draw at your doctor's or OB/GYN office and although preferred, you do not have to fast. Typical laboratories in Connecticut have a turnaround time of four to six days. Below is a summary of vitamin D levels cutoffs to determine if a vitamin D level is healthy.  

Vitamin D, 25-Hydroxy                Result           

<20 ng/mL                                     Deficient

20-30 ng/mL                                 Insufficient

>32 ng/mL                                     Optimal

Vitamin D deficiency has been linked to multiple sclerosis, rheumatoid arthritis, types I and II diabetes, heart disease, high blood pressure, dementia, cancer, and infectious diseases. However, there is insufficient evidence at this point to determine whether low vitamin D causes various diseases, exacerbates their progression, or if it is a product of the disease state.

Although >32 ng/mL is considered optimal, 40-50 ng/mL is when the body is able to store vitamin D. In other words, if your vitamin D levels are <50 ng/mL you are using your vitamin D as fast as you are making it, with no reserve. 

How much Vitamin D should I take?

The Institute of Medicine recommended daily dose allowance is 600IU and 800IU for adults over age 70. Many physicians find this threshold too low and advise to achieve 2,000IU per day. Regardless of the decision you and your physician make together, daily intake should not exceed the established upper normal limit of 4,000IU unless prescribed by a physician. 

A sunscreen with a SPF 8 can lower vitamin D production by 95 percent. It is advisable to allow sun exposure for a period of 20 minutes maximum before applying sunscreen. This ensures that vitamin D is synthesized, but that risk of skin cancer is also reduced with proper precautions.

If your vitamin D levels are optimal, then there is no need to add additional supplementation so long as your diet and sun exposure remains stable.  Please note that vitamin D levels greater than 150 ng/mL are considered toxic and lead to many potentially harmful adverse events. However, if you are insufficient, take steps to immediately correct the deficiency. For every 100 IU of vitamin D ingested, the blood level of 25-hydroxyvitamin D increases by 1 ng/ml.

Sun exposure for 20 minutes a day would yield 10,000 IU of vitamin D. A general consensus of the literature suggests that recommended direct sunlight exposure is 20min to arms and legs, or face, arms and hands, at least 3 times a week, with a UV Index of at least 3.

Vitamin D Facts

• Complete cloud cover reduces UV energy by 50 percent, while shade reduces it by 60 percent
• UVB radiation does not penetrate glass, therefore vitamin D is not produced through windows in the home or car
• Darker-skinned individuals, older adults, obese individuals and post menopausal women are at a greater risk for vitamin D deficiency
• Few foods are naturally high in vitamin D (herring, salmon, shitake mushrooms and tuna). Look for foods and drinks that are “fortified” such as milk, yogurt, oatmeals, cereals, and orange juice
• In Connecticut, the UVB radiation is not strong enough to make vitamin D from approximately November through April until about May
• Many people go the winter months unaware that they are vitamin D deficient. A blood test done during the winter can indicate a seasonal deficiency, in which case supplementation from November to May would be considered by your physician

The Department of Preventive Cardiology at Hartford Hospital is examining the effects of vitamin D supplementation (400IU vs. 4,000IU) on blood pressure.  The study is seeking men and women ages 18-50 yrs old with slightly elevated blood pressure (>120/80 mmHg), vitamin D deficiencyt (<20 ng/mL), and who are not currently being treated with blood pressure lowering medications. 

This is the perfect opportunity for those who are unsure of what their vitamin D levels are and would like to get it tested for free. Research participants will receive $150 for their time if they qualify and complete the study, with $25 for the initial blood draw. 

Call (860) 545-3454 or email aaugeri@harthosp.org for information.

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