Contrary to what you've likely heard countless times, vitamin D isn't really beamed into your skin straight from the sun. In fact, the "sunshine vitamin" isn't even a vitamin at all — it's actually a group of hormones, according to the Hormone Health Network.
What remains true, though? The nutrient we know as vitamin D is essential to your health. Unfortunately, many people don't get enough, and a deficit can affect everything from your energy levels to your risk for certain serious diseases.
Here's what you need to know about vitamin D and the important role it plays in your body, plus tips on how to boost your intake.
So, What Is Vitamin D?
At the scientific level, vitamin D is a group of hormones produced by a chemical reaction when you eat certain foods or absorb sunlight through your skin. However, it's easier to understand if we think of it like any other vitamin.
Vitamin D is fat-soluble, which means that — along with vitamins A, E and K — it is absorbed through the intestine in the presence of fat and can be stored in your system for a long time, explains a February 2016 report in The Clinical Biochemist Reviews.
There are two primary types of vitamin D:
- Vitamin D3, or cholecalciferol, is found in foods such as egg yolks and fatty fish. It's also the type your body makes when it's exposed to sunlight.
- Vitamin D2, or ergocalciferol, is present in some plants, such as some types of mushrooms, as well as yeast.
While both types of vitamin D are beneficial, "Vitamin D3 has been proven more effective in improving and sustaining your vitamin D levels," says Melaina Bjorklund, MS, RD, a practicing clinical dietitian at Penrose-St. Francis Health Services in Colorado Springs, Colorado.
Plus, a meta-analysis published in June 2012 in the American Journal of Clinical Nutrition confirms the superiority of vitamin D3 in helping humans achieve optimal levels of the nutrient and suggests that it should be the preferred form of supplementation.
Why Is Vitamin D So Important?
Vitamin D helps your body absorb the minerals calcium and phosphorus, which build up your bones and teeth and help keep them strong, according to the Academy of Nutrition and Dietetics.
Vitamin D also plays a role in nerve signaling and in regulating the immune system, Bjorklund says. In other words, the nutrient helps your muscles function properly and aids the body in fighting off invading bacteria and viruses.
As if that weren't enough, a lack of this mighty nutrient has been linked to a host of health issues.
Sunlight as a Key Source
Exposure to sunlight is crucial to help your body make vitamin D. In fact, according to a June 2019 article published in StatPearls, 50 to 90 percent of the vitamin D in your body is accrued through sun exposure.
If your climate has a lot of sunshine, the Vitamin D Council recommends getting outside a few times a week to soak it in. Keep in mind that you need to let the sun penetrate a large part of your body — not just your face and hands. The StatPearls paper notes that, on average, 20 minutes of sunshine daily with about 40 percent of your skin exposed is required to prevent vitamin D deficiency.
There's a catch, though: Wearing sunscreen decreases your absorption. However, sunscreen protects you from the sun's harmful ultraviolet rays, and foregoing it increases your risk of developing skin cancer, according to the American Academy of Dermatology (AAD).
For this reason, the AAD suggests that most people can and should get the vitamin D they need from a combination of D-rich foods and supplements, although you should speak with your doctor to determine the best approach for you.
Where to Find It in Foods
Many foods are fortified with vitamin D, explains Colette Raymond, a registered dietitian based in Colorado Springs, Colorado. Soy milk, orange juice, cereal and milk are some examples.
The vitamin can also be found naturally in cheese, beef, liver, egg yolks and fatty fish, such as canned and fresh salmon, mackerel, swordfish, halibut and eel, says Raymond. Mushrooms, particularly cremini and portabella varieties that have been exposed to UV light, as well as maitake mushrooms, also have a good amount of vitamin D2, according to the USDA nutrient database.
How Much Should You Really Be Getting?
The National Institutes of Health (NIH) suggests adults get 600 IU of vitamin D daily, while seniors over the age of 70 should get 800 IU per day. Some other organizations recommend higher doses, but according to the Mayo Clinic, taking in more than 4,000 IU a day is dangerous, and could result in side effects ranging from nausea and vomiting to heart rhythm problems and kidney damage.
However, about 1 billion people worldwide are deficient in vitamin D, according to the June 2019 article in StatPearls. And a whopping half of the global population has insufficient, but not medically deficient, levels of the nutrient.
Common Vitamin D Deficiency Symptoms:
- Frequent illness
- Bone or back pain
- Muscle pain
- Hair loss
Not everyone with a deficiency has obvious symptoms, though. Indeed, you may not know you're running low on D until bone loss has occurred, says Bjorklund.
Long-Term Health Implications
Low D levels may contribute to poor bone health — including osteopenia and osteoporosis — and serious injury from falls, especially in the elderly, according to comprehensive research published in August 2015 in the Singapore Medical Journal.
But the fix isn't quite as simple as just taking more vitamin D: Daily doses of 10,000 IU did not improve bone health compared to 4,000 or 400 IU in a three-year study of 311 older adults published in JAMA in August 2019.
What's more, researchers found an association between low vitamin D levels and limited mobility in older adults who recently underwent hip fracture surgery, according to a February 2020 study in The American Journal of Clinical Nutrition. The study also suggests a link between higher D levels and better walking rates and mobility.
Older adults with low D levels are also more likely to have impaired muscle strength, according to a study published October 2019 in Clinical Interventions in Aging. However, the researchers in this study didn't find an association between D levels and falls. But they did note that those who did moderate physical activity on a regular basis had significantly lower odds of impaired muscle function.
A chronic deficiency in vitamin D is associated with increased risk of cancer, type 2 diabetes and other immune system disorders, notes the February 2016 report in The Clinical Biochemist Reviews. And vitamin D may play a role in the prevention and treatment of some other chronic disorders, including hypertension and diabetes.
In fact, getting five to 10 times the recommended dose of vitamin D for six months may help slow the progression of type 2 diabetes in newly diagnosed patients and in people with prediabetes, a July 2019 study published in the European Journal of Endocrinology found_._
And on another brighter note, taking vitamin D supplements has been shown to help those who are ill with cancer. Research from Michigan State University published in June 2019 determined that supplemental vitamin D, taken in adequate amounts for at least three years, significantly lowered the risk of death among those with cancer compared to those that took a placebo. The study was based on information from more than 79,000 patients.
Who's Most at Risk for Vitamin D Deficiency?
Vitamin D deficiency more often shows up in older adults and people with darker skin pigmentation, according to the NIH. If you work indoors or habitually avoid the sun by staying in the shade or wearing protective clothing, you're also at risk.
Low calcium intake is also linked to low vitamin D levels because high-calcium foods like milk and yogurt are typically fortified with the vitamin. This means that people who are lactose intolerant, have a milk allergy or follow a vegan or ovo-vegetarian diet may not get enough vitamin D from the foods they eat. Those with nutrient absorption issues, such as Crohn's disease or inflammatory bowel disease, might be deficient as well.
People who live in northern climates with less exposure to UVB sunlight often don't get enough vitamin D, either.
If you believe you're not getting enough vitamin D, ask your doctor for a blood test to evaluate your levels. If you're deficient, you may benefit from taking a supplement.
- The Clinical Biochemist Reviews: "Fat-Soluble Vitamins: Clinical Indications and Current Challenges for Chromatographic Measurement"
- Academy of Nutrition and Dietetics: "What is Vitamin D?"
- American Journal of Clinical Nutrition: "Comparison of Vitamin D2 and Vitamin D3 Supplementation in Raising Serum 25-hydroxyvitamin D Status: A Systematic Review and Meta-Analysis
- Singapore Medical Journal: "Vitamin D Deficiency"
- Vitamin D Council: "How Do I Get the Vitamin D My Body Needs?"
- USDA Nutrient Database: "Vitamin D2 (ergocalciferol)(µg)"
- USDA Nutrient Database: "Vitamin D3 (cholecalciferol)(µg)"
- National Institutes of Health: "Vitamin D"
- StatPearls: "Vitamin D Deficiency"
- Hormone Health Network: "Vitamin D"
- American Academy of Dermatology: "Sunscreen FAQs"
- Michigan State University: "Vitamin D Could Help Cancer Patients Live Longer"
- Clinical Interventions in Aging: "Vitamin D Deficiency Is Associated With Impaired Muscle Strength And Physical Performance In Community-Dwelling Older Adults: Findings From The English Longitudinal Study Of Ageing"
- The American Journal of Clinical Nutrition: "Vitamin D deficiency is associated with reduced mobility after hip fracture surgery: a prospective study"