By Sharon Knight
Transplant Dietitian
Hartford Hospital Transplant Program
Vitamin D, also known as the “sunshine vitamin,” plays many roles in maintaining our good health. If you’re indoors most of the time and your skin never sees the light of day, then you might not be getting enough D. In fact, nearly half of the U.S. population is deficient.
Vitamin D is both a hormone (because your body can make it when it comes in contact with sunlight) and a vitamin (because you can obtain it from certain foods).
Getting vitamin D from your diet or from a supplement may be just as good as getting it from the sun, without having to worry about damage to your skin.
How Much Vitamin D Do I Need?
People ages 1 through 70 need 600 international units (or 15 mcg) per day and adults over 70 need 800 IU (or 20 mcg, or micrograms) each day, according to the National Institutes of Health.
Failing to meet your Recommended Dietary Allowance (RDA) for vitamin D can affect your entire body.
Researchers are now conducting randomized trials to determine if vitamin D levels affect the risk of COVID-19. People with vitamin D deficiencies typically have weakened immune responses, making them more vulnerable to coronavirus.
Your Bones
You will often see vitamin D added to a calcium supplement. What’s more, milk manufacturers in the United States fortify their milk (a calcium-rich drink) with vitamin D. There is a reason for this pairing — your bone health.
Vitamin D helps the body absorb calcium, at all ages, so getting enough vitamin D and calcium together can help prevent osteomalacia (soft bones) and osteoporosis (low bone mineral density) as you age, according to the NIH.
Your Muscles
The link between vitamin D and bone health is clear, but emerging research indicates that your muscles may also be affected by low vitamin D levels.
Muscle weakness has been noted in people with rickets and osteomalacia, according to April 2017 research published in Therapeutic Advances in Musculoskeletal Disease. The researchers also noted that low levels of vitamin D were associated with a reduction in muscle mass, which could be a contributor to falls and fractures as you age.
Your Joints
If you have joint pain or rheumatoid arthritis, it might be a good idea to have your vitamin D levels checked. Research has consistently found that people with rheumatoid arthritis are deficient in vitamin D. Whether an inflammatory condition causes vitamin D deficiency or whether vitamin D deficiency contributes to inflammatory conditions is still not known.
Your Skin
Vitamin D deficiency may play a role in your skin health, too. If you have severe acne, you might want to get your vitamin D checked as well.
What’s more, people with severe acne were more likely to have a vitamin D deficiency. It was also noted that, in people with acne, reduced vitamin D levels increased the volume of oil glands in the skin.
Your Immune System
Vitamin D plays many roles in keeping your immune system strong. The nutrient dampens the inflammatory response associated with illness and increases immune proteins, according to the Harvard T. H. Chan School of Public Health, and that’s good news when you’re working to stay healthy.
Testing for a Vitamin D Deficiency
The above-mentioned symptoms associated with vitamin D deficiency might alert you that your levels are low, but a blood test is the only way to confirm that.
You want your vitamin D levels to be between 50 and 125 nmol/L, or nanomoles per liter. Below 50 nmol/L is considered insufficient and levels above 125 nmol/L is not recommended.
If your vitamin D is low, your doctor will probably prescribe you a supplement and your dose will be determined per your current levels. Up to 4,000 IU of vitamin D is safe for most healthy adults, the Mayo Clinic suggests, but it’s still good practice to follow your doctor’s dosage advice to get your vitamin D levels within normal range.
Too much supplementation with vitamin D is not the way to go either. It can cause excessive calcium in your blood and this can lead to heart problems, blood vessel damage and impaired kidney function, according to the NIH.
How Your Location Plays a Role in Your Vitamin D Levels
If you live too far north, you may not be able to get enough vitamin D in the winter.
How to Get More Vitamin D
Getting your vitamin D is a double-edged sword: Too much sun and you run the risk of skin cancer, and too little runs the risk of vitamin D deficiency.
Spending 15 to 20 minutes in the sun twice a week with 40 percent of your skin exposed is enough to prevent deficiency, according to January 2010 research published in the International Journal of Health Sciences.
When choosing a supplement, do you go for vitamin D2 or D3?
Unlike D2, D3 is naturally produced in the body when your skin comes in contact with sunlight. research suggests that D3 supplements can raise blood concentrations of the vitamin more and sustained those levels longer than D2, according to the Harvard T.H. Chan School of Public Health, so opt for D3 when you can.
Vitamin D Amounts in Food
| Source | Amount of Vitamin D | Percent Daily Value (based on 800 IU) |
| Rainbow trout, 3 ounces | 645 IU | 81% |
| Salmon, 3 ounces | 570 IU | 71% |
| 2 percent milk, fortified with vitamin D | 120 IU | 15% |
| Fortified breakfast cereals | ~80 IU | 10% |
| Sardines, 2 whole | 45 IU | 6% |
| One egg yolk | 44 IU | 6% |
| Canned tuna in water, 3 ounces | 40 IU | 5% |
Source: NIH
Sharon Knight is a transplant dietitian with the Hartford Hospital Transplant Program.
