Vitamins are important for our overall health and well-being. Learn the signs of low levels of vitamin D and what you can do about it.

Published: June 3, 2024

You know vitamins are good for you, and you might know humans get vitamin D from exposure to the sun’s warming rays. There are also vitamin D supplements sold over the counter. Low vitamin D levels in your body can make you feel tired, cause bone pain or cause muscle weakness.

What does vitamin D do?

“Vitamin D is an antioxidant and anti-inflammatory. It protects the brain cells and supports immune health. Vitamin D also regulates calcium and phosphate in the body,” said Joshua H. Brandon, M.D., a family medicine physician with Norton Community Medical Associates.

Calcium is important for bone health, but the body needs vitamin D present to absorb the calcium, according to Dr. Brandon.

How do you get vitamin D?

This essential nutrient is found in some foods, such as fatty fish like salmon or mackerel, as well as in fortified milk and cereal that have vitamin D added.

“Your body makes some vitamin D when the skin is exposed to direct sunlight,” Dr. Brandon said. “A chemical in the skin converts sunlight to active vitamin D so it can be used.”

Children typically don’t have low levels of vitamin D, since they spend more time outdoors than adults. Since research has shown that prolonged exposure to the sun can damage DNA in the cells, cause skin cancer and prematurely age skin, adults shouldn’t stop taking skin precautions while in pursuit of vitamin D from sunlight.

“Don’t skimp on the sunscreen or go without a hat to get more vitamin D,” Dr. Brandon said. “The benefits of protecting the skin from sun damage far outweigh any negatives, and you still can maintain healthy vitamin D levels without abusing your skin.”

Besides the sun and some foods, the best way to boost vitamin D is with supplements.

“Vitamin D is sold over the counter, meaning you don’t need a prescription,” Dr. Brandon said. “Adults ages 18 and older will need anywhere between 15 and 20 micrograms a day. It depends on your gender, pregnancy status and age.”

How can I tell if I have vitamin D deficiency?

Signs of vitamin D insufficiency include:

1. Fatigue
2. Poor sleep
3. Depression or feelings of sadness
4. Hair loss
5. Muscle weakness that affects arms, legs, or ability to walk
6. Loss of appetite

Low vitamin D can lead to bone-related conditions, such as softening of the bones (osteomalacia), weak or brittle bones (osteoporosis), and an increased risk for breaks. 

Risk factors for low vitamin D levels

For most people, low vitamin D levels are not a problem. Most adults get most of their recommended daily dose of vitamin D through their diet. The rest can be made up with sun exposure. (Vitamin D is sometimes called the sunshine vitamin.) 

Other risk factors include:

• Having darker skin: Darker skin tones have a harder time converting sunlight into vitamin D. 
• Having a higher body weight: Although researchers don’t know exactly why, obesity is associated with low vitamin D levels. 
• Access to sunlight: People who are homebound or who don’t get outside often can be at a higher risk for low vitamin D.
• Being older than 65: Your body’s ability to make vitamin D decreases as you age. 
• Weight loss surgery: Having a weight-loss procedure can affect how well vitamin D from food is absorbed by the body.

Can you have too much vitamin D?

It’s important to have the right amount of vitamin D, because it’s possible to have too much, according to Dr. Brandon.

“Vitamin D toxicity, also called hypervitaminosis, can make you feel dizzy and nauseated,” he said. 

Left untreated, vitamin D toxicity can cause a buildup of calcium in the blood. This can cause bone pain or kidney issues, including kidney stones.

What are the risks of having a low vitamin D level?

Some people with chronically low vitamin D may have:

• Increased risk of death from heart disease
• Mental difficulties, especially in older adults
• Bone pain and osteoporosis
• High blood pressure
• Increased risk of some cancers

How can I tell if I have a vitamin D deficiency?

The signs of low vitamin D can be subtle.

“A simple blood test will tell your doctor if you need a boost in vitamin D,” Dr. Brandon said. “Vitamin D is measured in nanograms per milliliter (ng/mL). We recommend between 20 and 50 ng/mL, roughly. Again, it depends on several factors. Your doctor can help you determine what is a good level for you.”

When you visit your primary care doctor, ask about your vitamin D status. Annual checkups with your health care provider may help you avoid a low vitamin D level. You may need a vitamin D supplement, with or without calcium. Eating more vitamin D-rich foods doesn’t typically correct an inadequate vitamin D level, so you likely will be advised to take a daily pill.

“We want to set you up for a lifetime of health, and that starts with a baseline look at aspects of your current health, such as blood pressure, cholesterol, or vitamin D levels,” Dr. Brandon said.