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

According to Dr. Sangwan, the best way to determine whether or not you have a vitamin D deficiency is to visit your primary care doctor and ask for a test called the 25-hydroxy vitamin D test. This test will tell you how much vitamin D is in your body.

Good levels of vitamin D should be anywhere between 50 to 75 nanograms per deciliter, says Dr. Sangwan. Since you’ll be getting this test at your doctor’s office, they’ll read you the results and explain whether or not your vitamin D levels are adequate.

If you’re unable to see a doctor, however, there are also a handful of symptoms that can indicate you’re deficient in vitamin D.

What are the symptoms of vitamin D deficiency?

1. Brain fog

Have you ever felt like your brain just… isn’t working? That’s what the medical community refers to as brain fog. A vitamin D deficiency can lead to this. In fact, a 2020 study found that having low vitamin D levels was associated with cognitive impairment and dementia.

2. Joint pain

Joint pain is largely due to inflammation. Because vitamin D has anti-inflammatory properties, a lack of vitamin D can cause more inflammation. This, in turn, may lead to joint pain.

3. Depression

Dr. Sangwan and Dr. Greene agree that a lack of vitamin D may also cause depression. “Low vitamin D affects serotonin synthesis in the brain, which can lead to depression and seasonal effectiveness disorder,” says Dr. Sangwan.

Dr. Greene adds that vitamin D is a co-factor in producing dopamine, meaning that in order for your body to produce the pleasure hormone (a common nickname for dopamine), vitamin D must be present.

4. Insomnia

Vitamin D stimulates the pineal gland to produce melatonin, says Dr. Greene. If you're not getting enough vitamin D—particularly through sunlight—this may lead to a lack of melatonin. Considering that melatonin is what stimulates our sleep behavior, a vitamin D deficiency can also cause insomnia.

5. Low immune function

“Vitamin D helps your immune system to be strong enough to fight colds, flu, and even Covid,” says Dr. Sangwan