By Andrea Boldt  (Image Credit -Getty Images/Ridofranz)

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:

  1. 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.
  2. 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, RD, a practicing clinical dietitian at Penrose-St. Francis Health Services in Colorado Springs.

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.

Normal Vitamin D Levels

Levels greater than or equal to 50 nmol/L (or greater than or equal to 20 ng/mL) are generally considered adequate for bone and overall health, according to the National Institutes of Health (NIH).

Adequate intake levels of vitamin D vary according to age. The recommended dose for people between the ages of 1 to 70 is 10 mcg each day. Adults older than 20 need 15 mcg of vitamin D to stay healthy.

Benefits of Vitamin D

If you’re keeping a mental list of which vitamins are worth tracking, vitamin D is definitely one of them. From your bones to your brain to your gut, vitamin D’s benefits to your health reach far and wide.

1. Vitamin D Can Support Bone Health

Vitamin D is necessary for helping your body build strong and healthy bones, according to the Mayo Clinic. Your body depends on vitamin D to absorb calcium, which is the main component found in your bones.

That’s why a lot of breakfast cereals are fortified with vitamin D. Typically, cereal is eaten with milk, which is a good source of calcium, according to the NIH. So, when you eat these two together, you’re getting the full bone-health benefit.

2. It Benefits the Immune System

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.

3. Vitamin D Is Linked to Improved Muscle Health

Getting adequate vitamin D (more on that below) is also necessary for your muscle health and strength, according to a November 2012 study published in Sports Health.

Increasing your vitamin D can help improve your muscle protein synthesis and ATP concentration, a compound that supplies your body with the energy needed for muscle function.

Vitamin D supplementation can also help reduce inflammation or pain, making it helpful for athletes, according to the above-mentioned study. Increasing vitamin D levels is tied to helping improve athletic factors like strength, jump height, jump power, exercise capacity and physical performance.

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4. Vitamin D Is Linked to Better Brain Health

Especially early in life, vitamin D plays a big role in your overall brain development and function, according to a July 2018 study published in Cureus.

Even for adults, vitamin D supports normal brain function and development, according to a November 2017 study in the International Journal of Molecular Sciences. Unfortunately, despite speculation, there isn’t any firm evidence to suggest that vitamin D can help prevent neurodegenerative conditions or diseases.

5. Vitamin D Is Tied to Good Gut Health

The vitamin can also help regulate your gut health, according to an August 2018 study in the Journal of Research in Medical Sciences.

While you shouldn’t try any treatments without a doctor’s approval, vitamin D supplementation may help regulate gastrointestinal inflammation and IBS and may even help treat colitis (a chronic digestive disease).

Increased vitamin D consumption has also been associated with reduced risk for colitis caused by immune checkpoint inhibitors, a type of drug often used in cancer treatment, according to a June 2020 study published in the American Cancer Society Journals.

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, get 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

There aren’t many foods high in vitamin D but the vitamin can 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.

Some processed items are fortified with D, explains Colette Raymond, a registered dietitian based in Colorado Springs. Soy milk, orange juice, cereal and milk are some examples.

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.

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How Much Should You Really Be Getting?

The National Institutes of Health (NIH) suggests adults get 600 IU of vitamin D daily, while adults 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
  • Fatigue
  • 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.

Can Low Vitamin D Cause Fatigue?

A vitamin D deficiency may cause a lack of energy, including depression and fatigue, according to the Cleveland Clinic. A vitamin D deficiency is characterized as levels that fall below 50 nmol/L.

Seasonal affective disorder (SAD) occurs during certain seasons of the year, specifically the fall and winter, and is characterized by feelings of depression, fatigue and sleepiness. It is believed that a lack of sunlight and a deficiency of vitamin D may be the cause of this disorder. When the winter months lose sunlight, you may begin to lack vitamin D, which increases melatonin and fatigue.

Long-Term Health Implications

1. Vitamin D and Bone and Muscle Health

Low D levels may contribute to poor bone health — including osteopenia and osteoporosis — and serious injury from falls, especially in older people, 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.

2. Vitamin D and Cancer

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.

And on a 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.

3. Vitamin D and Blood Sugar

Observational studies suggest an inverse relationship between vitamin D and the risk of type 1 and type 2 diabetes, according to Oregon State University.

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​.

A May 2004 study in the American Journal of Clinical Nutrition found that people with a vitamin D deficiency are at higher risk of glucose intolerance and metabolic syndrome.

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.

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