How to Tell if You Have a Vitamin D Deficiency—and What to Do About It

A woman with her hand up, wearing a gray sweatshirt against a beige background.

One great thing about the warmer months of the year is that it’s way easier for our bodies to get enough vitamin D—if we’re spending more time in the sun, that is. It’s important to make sure you’re getting enough vitamin D each day because it plays many important roles in helping us stay in good health, including hormone regulation, maintaining bone health, and keeping our immune system running strong.

Sunlight is one of the simplest ways to increase vitamin D levels in the body. Many people can get an adequate amount of vitamin D with 15-30 minutes of sun exposure. But sun exposure isn’t the only way to get a healthy dose of vitamin D—you can also obtain it from foods like oily fish, milk, and eggs or through supplements.

Most people need around 600 to 800 IU of vitamin D per day, though some people need more. This includes people with dark skin, older adults, people who are rarely in the sun, and people with conditions that limit fat absorption.

When we don’t get enough vitamin D, our bodies feel the effects. Vitamin D deficiency comes with a number of symptoms, from fatigue to muscle pain to hair loss and even behavioral changes.

Research shows that a fairly significant percentage of people are deficient in vitamin D, so if you have any concerns about vitamin D deficiency, you’re going to want to see a doctor. There’s a good chance they may recommend a blood test to check your vitamin D levels—anything below 20 ng/ml is considered low.

Here are some signs you may be deficient in vitamin D.


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People with really low levels of vitamin D may experience fatigue, research shows. Sometimes this fatigue can be pretty severe.

Taylor Engelke, who is a registered dietitian nutritionist, explains that fatigue can also be a symptom of having too much vitamin D, rather than too little.

“[Vitamin D] levels too high in the bloodstream are greater than 250nm/mL, which would be possible if someone was taking supplements higher than 10,000 IU daily,” she says.

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Muscle Weakness and Muscle Pain

Some studies suggest that vitamin D deficiency could contribute to muscle pain and weakness. If you’re experiencing a lot of muscle pain and are unsure of the cause, you may want to speak with a healthcare professional.

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Hair Loss

“Low vitamin D levels have been linked to hair loss and the slowing of hair growth due to the follicles being stunted,” Engelke explains.

She adds that “an autoimmune condition called alopecia has been linked to vitamin D deficiency, which is where hair all over the body stops growing due to follicle death.”

So why exactly can hair loss occur due to vitamin D deficiency? Basically, vitamin D is metabolized in our skin by cells called keratinocytes, which produce the keratin that keeps our hair in good health. When the body isn’t getting enough vitamin D, the keratinocytes may have trouble facilitating hair growth, and you could end up experiencing hair loss.

It’s important to realize that hair loss isn’t due to vitamin D deficiency most of the time. More frequently, hair loss is due to hormones, genetics, pregnancy, trauma, or surgery.

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You Get Sick Frequently

Vitamin D plays a big role in immunity. Some research shows that vitamin D deficiency is associated with a weaker immune system. So If you get sick frequently, it’s important to realize that you could be deficient in vitamin D. This is definitely a symptom worth checking in with your doctor about.

In addition to getting sick more frequently, vitamin D deficiency is also associated with an increase in autoimmune conditions and increased susceptibility to infections.

Vitamin D’s role in immunity is in part due to how white blood cells develop and function, Engelke explains.

“Most people can benefit from 4000IU daily supplementation to fight off upper respiratory tract infections and inflammation that can lead to more chronic diseases,” says Alana Kessler, who is a registered dietitian and founder of Be Well by AK.

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Bone Pain

Vitamin D is needed to help our bodies absorb calcium. “In essence, it acts as an enzyme to move calcium into the bones,” Kessler explains.

Osteoporosis, bone pain, osteomalacia (soft bones), and other skeletal, connective tissue, and muscular issues can occur without vitamin D.

“Without sufficient vitamin D, the parathyroid gland will take calcium from the bones because it can not properly be metabolized without it,” she says.

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Depression and other Behavioral Changes

“There is no medical research that vitamin D is either a cause or a fix for depression, but when the system is not working properly, the body is over-functioning systemically,” Kessler says. “This can lead to fatigue and brain fog and inflammation.”

She adds that if our bones aren’t receiving the calcium they need, and the muscles and connective tissue are running in overdrive to support the skeleton; people may experience exhaustion simply from everyday activities. “Over time, this can impact mental health, hormone balance, and overall wellness.”

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Weight Gain

Current research doesn’t establish a clear link betweenvitamin D deficiency and weight gain, but there is an established association between low vitamin D levels and obesity. Researchers suggest that this may be because people with obesity may require more vitamin D to achieve the same level in the body as people who do not have obesity.

Further research is needed before we can declare any definitive statements about the link between vitamin D and weight.

Vitamin D plays many important roles in keeping us healthy—so it’s essential to make sure you’re getting enough. When you’re deficient in vitamin D, you can experience symptoms throughout your body, ranging from behavior changes to bone and muscle pain, fatigue, increased susceptibility to infection, and more. If you think you might be deficient or have any other related concerns, definitely see your doctor to have those vitamin D levels checked.


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