One of the most common nutrient deficiencies worldwide is vitamin D. A vitamin D deficiency affects bones, muscles, and many other systems. It’s most common among seniors and folks who have a darker skin tone. Fortunately, a vitamin D deficiency is preventable and generally easy to deal with once you know about it.

What Is Vitamin D and Why Is it Important?

Vitamin D is an essential nutrient vital for normal bone development as it’s needed to maintain the balance of calcium in the blood and bones. Vitamin D is also important for the healthy function of muscles, the nervous system, and the immune system.

The easiest way to get enough vitamin D is through sun exposure. That is, when bare skin is exposed to daily sunlight, the body can synthesize the nutrient. Unfortunately, many of us don’t get enough sunlight either due to where we live, due to our complexion (i.e., skin color), or because of the importance of protecting the skin from excess sunlight, as too much sun can lead to an increased risk of skin cancers and accelerate aging.

Signs of a Vitamin D Deficiency

A severe or chronic vitamin D deficiency decreases the absorption of calcium and phosphorus by the intestines. This can result in low calcium levels in the blood, which can then lead to an overactive parathyroid response. This can result in:

• Muscle weakness and pain
• Bone demineralization (when the bone breaks down quicker than it forms), leading to loss of bone density and an increased risk of broken bones
• Soft bones in adults and rickets in children, which can lead to bone pain and joint deformities
• Hair loss

A vitamin D deficiency can affect anyone—from infants to seniors—and affects over one billion people worldwide. As mentioned, it’s most prevalent in people with darker skin tones (due to their higher skin melanin content) and those living in areas with less sun exposure or those who dress most conservatively (covering most of the skin). Vitamin D deficiency can also result when the body doesn’t properly absorb or use vitamin D due to:

• Being older
• Medical conditions (e.g., cystic fibrosis, Crohn’s, celiac, or kidney disease, which can decrease nutrient absorption)
• Some medications (e.g., laxatives, steroids, statins, and weight-loss drugs)
• Being overweight or obese
• Being underweight (such as due to eating disorders)
• Weight-loss surgery (weight-loss surgery can reduce the size of the stomach, which makes it more difficult to absorb nutrients from foods. So, it’s vital to measure nutrient levels and supplement if they aren’t optimal after surgery.)
• Dietary restrictions, such as avoiding dairy or fish
• Lack of access to sunlight year-round (i.e., those people who live closer to the poles and farther from the equator)
• Working and playing indoors (and not getting outside regularly)

An estimated 35 to 42% of adults in the U.S. are deficient in vitamin D. That number climbs to 63% of Hispanic adults and 82% of African American adults. Even for those who aren’t deficient, there’s a risk of having suboptimal levels, which may lead to:

• Feeling tired
• Increased risk of heart issues, including heart attacks, heart failure, peripheral arterial disease, and strokes
• Increased risk of high blood pressure
• Increased risk of diabetes
• Poor immune functioning, which can lead to more frequent or lasting illnesses and infections, including colds or the flu
• Bone pain
• Lower back pain
• Muscle weakness
• Decreased mood, especially in older adults, including depression and anxiety
• Cognitive impairment, including lowered executive function such as reasoning or flexibility, decreased attention, slowed processing, and memory loss
• Weight gain, which can increase the risk of obesity
• Slowed or impaired healing
• Increased risk of multiple sclerosis

What to Do If You Have a Vitamin D Deficiency

As usual, prevention is the best cure. It’s important to strive for optimal levels of vitamin D. However, optimal levels have been debated depending on which organization you look at. For example, the Institute of Medicine (IOM) recommends between 12.5 and 20 mg/mL for healthy bones. Anything below 20 is considered a deficiency. However, the highly respected Endocrine Society recommends a much higher level. They suggest the minimum is 30 ng/mL. And to ensure optimal levels, they recommend 40 to 60 ng/mL for adults and children.

To obtain and maintain optimal levels, you can get more sun exposure without the risk of burns. That is, spend a minimum of ~15 minutes in the sunshine with the face, arms, and legs exposed several times a week. People with darker skin may need to spend even more time in the sun, and people with very pale skin may need less to avoid burning. If you’ll be in the sun longer, use a sunscreen with an SPF of at least 15 and preferably 30 to prevent burns and damage to the skin.

There are also some foods that provide vitamin D, such as:

• Fatty fish like wild-caught salmon, halibut, mackerel, herring, and sardines
• Canned tuna
• Cod liver oil
• Beef liver
• Egg yolks
• Mushrooms, especially morels and other wild-grown mushrooms
• Vitamin D-fortified foods and drinks like milk, orange juice, oatmeal, cereals, and yogurt

We can also get vitamin D from quality vitamin D supplements. The recommended daily amount is around 800 to 2,000 IU from food and/or supplements.

Because vitamin D is a fat-soluble vitamin, you can also have too much, which is why yearly blood tests are recommended—to ensure you have optimal levels without going too high. At-home tests are also available, making checking vitamin D levels easier and more convenient.

Too much vitamin D in the body is rare, but it does happen and can lead to:

• Nausea
• Increased thirst
• Increased urination
• Poor appetite
• Constipation
• Weakness
• Confusion
• Impaired balance or coordination
• Impaired speech

Vitamin D Deficiency: A Wrap-up

You’re much more likely to have a vitamin D deficiency than too much. While vitamin D deficiencies are very common, even in the U.S., symptoms can vary widely and are often subtle, making it difficult to determine. A blood test can tell the tale and let you know if your levels are suboptimal or deficient. And fortunately, addressing a vitamin D deficiency once you know about it is fairly easy and can be highly beneficial.

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