Also known as the "sunshine vitamin," vitamin D 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.
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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 IU (or 15 mcg) per day while adults over 70 need 800 IU (or 20 mcg) each day, according to the National Institutes of Health (NIH).
Failing to meet your Recommended Dietary Allowance (RDA) for vitamin D can affect your entire body, from your immune system to your skin and more.
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.
Getting enough vitamin D is associated with reducing viral infections by strengthening the physical immune response of the body and helping to reduce inflammation, according to April 2020 research published in Nutrients.
However, the study authors note that thorough randomized controlled trials and large population studies need to be conducted in order to solidify these findings.
In addition, people with low vitamin D levels reported more coughs, colds and respiratory infections. Children with rickets caused by low vitamin D suffer more respiratory infections over those with sufficient vitamin D, per the Harvard T. H. Chan School of Public Health.
You will often see vitamin D added to a calcium supplement. What's more, milk manufacturers in the U.S. 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.
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.
This does not mean that supplementing with vitamin D will guarantee you stronger muscles. According to a June 2018 review study published in Bone Reports, supplementing with vitamin D in deficient athletes showed mixed results. Some athletes showed improved performance, but others did not.
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, according to a January 2018 review published in the Journal of Natural Science, Biology, and Medicine. Plus, people in remission have higher levels of vitamin D whereas those experiencing the worst symptoms had the lowest levels of D.
Whether an inflammatory condition causes vitamin D deficiency or whether vitamin D deficiency contributes to inflammatory conditions is still not known, per a January 2015 review published in Dermatoendocrinology.
It's worth noting that researchers found that in six out of eight randomized controlled trials, supplementation with vitamin D3 reduced markers of inflammation.
Vitamin D deficiency may play a role in your skin health, too. If you have severe acne, scheduling an appointment to get your vitamin D levels checked might help clear your visage.
Inflammation plays a role in the development of acne and low vitamin D levels can contribute to inflammation. In fact, vitamin D-deficient people with acne who added a vitamin D supplement to their daily routine (they took 1000 IU per day for two months) saw improvement in inflammatory lesions, an August 2016 study published in PLOS One found.
What's more, people with severe acne were more likely to have a vitamin D deficiency, an October 2019 meta-analysis published in Australasian Journal of Dermatology found. It was also noted that, in people with acne, reduced vitamin D levels increased the volume of oil glands in the skin.
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And that's not all: Vitamin D deficiency may also play a role in atopic dermatitis and psoriasis, according to the October 2019 review.
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. 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 — specifically, if you live at latitudes above 37 degrees north or below 37 degrees south of the equator.
In the U.S., that line is near the southern borders of Missouri, Kansas and Colorado. Below the 37th parallel, you have a better chance of getting good vitamin D from the sun in the winter, according to Harvard Health Publishing.
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, and you run the risk of vitamin D deficiency.
But there's a sweet spot: 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. Robust 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
Amount of Vitamin D
Percent Daily Value (based on 800 IU)
Rainbow trout, 3 ounces
Salmon, 3 ounces
2 percent milk, fortified with vitamin D
Fortified breakfast cereals
Sardines, 2 whole
One egg yolk
Canned tuna in water, 3 ounces
While you may have heard that mushrooms contain vitamin D, that's not always the case. Only mushrooms exposed to UV light after harvesting — or naturally wild mushrooms such as chanterelles, maitake and morels — contain D.
They're usually labeled "UV-treated" or "high in vitamin D," according to the University of California, Berkely.
- National Institutes of Health: "Vitamin D"
- Therapeutic Advances in Musculoskeletal Disease: "The Role of Vitamin D in Maintaining Bone Health in Older People"
- Bone Reports: "Vitamin D and Muscle"
- Mayo Clinic: "Osteoporosis"
- Harvard Medical School: "Vitamin D and Your Health: Breaking Old Rules, Raising New Hopes"
- International Journal of Health Sciences: "Vitamin D Deficiency- An Ignored Epidemic"
- Journal of Natural Science, Biology, and Medicine: "Assessment of Vitamin D in Rheumatoid Arthritis and Its Correlation with Disease Activity"
- Dermatoendocrinology: "Vitamin D and Inflammation"
- Harvard T. H. Chan School of Public Health: "Vitamin D"
- Nutrients: "Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths"
- PLOS One: "Comparison of Vitamin D Levels in Patients with and without Acne: A Case-Control Study Combined with a Randomized Controlled Trial"
- Australasian Journal of Dermatology: "Vitamin D Deficiency in Patients With Acne Vulgaris: A Rystematic Review and Meta‐Analysis"
- Harvard Medical School: "On Call: Vitamin D2 or D3?"
- University of California, Berkely: "Mushrooms and Vitamin D"
- Cereus: "Prevalence of Vitamin D Deficiency and Associated Risk Factors in the US Population (2011-2012)"