Our Bodies Need Vitamin D—Here's What Happens When We Don't Get Enough

Photograph: Getty Images; Collage: Gabe Conte

As far as nutrients go, vitamin D is one of the most widely useful—but oft-overlooked—things we put in our bodies. For instance, “there are more than 200 known functions of vitamin D in the body,” says osteopathic physician Ryan Greene, DO. Sure, it’s great for building your bone strength, but it’s also necessary for so many other reasons. This is precisely why you don’t want to have a vitamin D deficiency.

Neil Paulvin, DO, a New York-based longevity and regenerative medicine doctor, echoes this sentiment, saying that “vitamin D is extremely integrated into our bodies and helps it in a lot of different ways,” says Dr. Paulvin.

Below, we get into what vitamin D is, the symptoms of vitamin D deficiency, and how to provide your body with enough vitamin D for optimal function.

What is vitamin D?

Vitamin D is a fat-soluble vitamin and hormone that includes vitamins D1, D2, and D3. “It’s important to note that vitamin D behaves more like a hormone, which is a chemical made by the body that stimulates and controls functions of other parts of the body,” says internal medicine physician Neha Sangwan, MD, who is also the founder of the private practice, Intuitive Intelligence.

As Dr. Paulvin mentioned, vitamin D plays an integral role (or several) in the human body. “It helps build our immune system and is needed to help regulate our hormones,” says Dr. Paulvin. “It also helps support our bones, decreases inflammation, and regulates cholesterol formation,” he adds.

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.

Why is it bad to have a vitamin D deficiency?

It’s bad to have a vitamin D deficiency because this can negatively affect your longevity, your bone and muscle strength, your oral and dental health, and even your heart health.

Though it’s rare, a severe vitamin D deficiency can lead to a disease called rickets, also known as osteomalacia. Typically, the disease affects children—making it hard for their bodies to absorb calcium, thus rendering their bones weak.

Luckily, it’s relatively simple to prevent a vitamin D deficiency in children and adults.

How can I prevent a vitamin D deficiency?

1. Spend time in the sun

According to the experts, this is one of the best ways to ensure that your body is getting enough vitamin D. However, it’s still important to wear your sunscreen when you’re out in the sun. Contrary to sunscreen conspiracy theories, there is no empirical evidence that applying sunscreen inhibits your skin from absorbing the UV rays that are necessary to produce vitamin D.

2. Eat foods with a high amount of vitamin D

As you may remember from those “Got milk?” ads, milk has tons of vitamin D. That said, you can’t go for a milk alternative like soy, almond, or oat. In order to get the full serving of vitamin D, Dr. Paulvin says you need to reach for the dairy.

Other foods that are great for combating vitamin D deficiency? Bananas, beans, broccoli, Brussels sprouts, and all types of nuts. Fatty fish that live in shallow water—like herring, sardines, and salmon—are also a great source of vitamin D.

A note here: It’s unlikely that you’ll reach the necessary levels of vitamin D just from eating foods that contain it. The experts we consulted also advocate taking a vitamin D supplement.

3. Take a supplement

One thing that Dr. Paulvin notes about vitamin D intake, however, is that you want to be sure you’re getting vitamin D3—as opposed to the other two types of vitamin D.

“D3 is more used by the body, which is why that’s what you want to opt for,” Dr. Paulvin adds. If you’re taking a supplement, the type of vitamin D3 that it contains will be written directly on the label. Additionally, Dr. Sangwan says that you’d be wise to take a supplement that combines D3 with vitamin K2—a vitamin that helps to metabolize calcium.

“Vitamin K2 helps your body transport the vitamin D into your bones and teeth, rather than letting it sit in your arteries and other soft tissues,” she says. “It's almost like vitamin K2 is the transport that gets the D3 to where it's needed.”

Dr. Greene suggests supplements from Lifeforce or Thorne ($28) because they’re high-quality sources that are approved by the National Sanitation Foundation, a public health and safety organization that tests, inspects, and certifies products. Moreover, they both offer vitamin D3 coupled with vitamin K2.

Regardless of how you choose to take your vitamin D, Dr. Sangwan suggests getting the 25-hydroxy vitamin D test to ensure that your body is getting as much as it needs.

Originally Appeared on GQ