We’re in the thick of wintertime: the days are short and dark, it’s chilly outside, and all you probably want to do is get cozy under a blanket and curl up with a good book (or, winter rom-com!) And while we love the snuggly feels this time of year offers, not getting enough sun puts us at risk of having low vitamin D levels.

Vitamin D is a fat-soluble vitamin that your body uses to absorb calcium, so it plays a key role in building and maintaining your bones. It’s also involved in immune and muscle function and has anti-inflammatory and neuroprotective properties, says the Mayo Clinic. So yeah, it’s kind of a big deal.

So if you’re not getting the recommended 600 IU (or 15 micrograms) of vitamin D per day, what happens? Possibly nothing, if you’re just falling a little short. “There are usually no signs or symptoms that someone may be deficient in vitamin D,” says David Cutler, M.D., a board-certified family medicine physician at Providence Saint John’s Health Center in Santa Monica, CA.

But if you have a severe or chronic deficiency in vitamin D and are regularly not getting enough of the vitamin through sunlight, you’re likely to have more noticeable symptoms, says Kimberly Gomer, R.D.N., a registered dietitian based in Miami, FL.

But what do noticeable symptoms even look like? Below, you’ll find all the signs of a vitamin D deficiency, plus how to get more vitamin D if your body isn’t getting enough.

More urinary tract infections

Being low in vitamin D seems to significantly up the risk for urinary tract infections, per a meta-analysis of nine studies published in the Annals of Clinical & Laboratory Science. “Adequate to optimal levels of vitamin D are critical for healthy immune function,” Gomer says. That includes stimulating the production of antimicrobial compounds (aka substances that stop or eliminate the growth of pathogens like bacteria and viruses) to fight off UTI-causing bacteria, the analysis authors note.

Pale skin

Feel like you’ve lost some color? The change in your complexion might happen from more than just the weak winter sun. “Pale skin can also be a symptom of vitamin D deficiency,” Gomer says.

Hair loss

Clumps of hair in your brush, on your pillow, or by the shower drain are usually a sign that something’s up health-wise. And in some cases, it could be low vitamin D. The nutrient plays a role in stimulating hair follicle growth, and inadequate levels are tied to hair loss, notes a Journal of Cosmetic Dermatology review.

Muscle weakness or spasms

In addition to supporting your bones, vitamin D’s role in calcium absorption helps prevent a condition called hypocalcemic tetany—the medical term for involuntary muscle contractions that cause spasms, cramping, and weakness. So if you’re consistently feeling twitchy or weak, it’s possible that your vitamin D levels could be to blame.

Changes in mood

Sure, it could be the fact that the sun is setting earlier and earlier these days. Or it could be that you’re not getting enough vitamin D. (Or hey, maybe both!) “Vitamin D has a role in regulating serotonin and melatonin, which affect mood,” Gomer says. FYI, serotonin regulates mood, while melatonin plays a role in sleep. Getting enough of both is thought to play a role in the prevention of mood disorders like major depressive disorder, notes a Current Nutrition Reports paper. That said, the less serotonin and melatonin your body produces, the higher your risk of experiencing low mood symptoms, like sadness or irritability.

Frequent Colds

Low vitamin D could be to blame if you’re getting more coughs and sniffles than usual lately. The vitamin boosts your body’s defenses against infectious illnesses, including respiratory infections, according to a paper published in The Lancet Diabetes & Endocrinology. Essentially, it can help you fight off germs or bounce back faster after you’ve been exposed to pathogens like bacteria or viruses. “We saw during the COVID pandemic, before a vaccination was available, that those with low Vitamin D levels had poor outcomes compared to those with sufficient or optimal levels,” Gomer points out. Case in point.

Fatigue

Feeling exhausted all the time is one of the most common signs that someone’s short on D, Gomer says. Vitamin D seems to be involved in sleep regulation, including the production of sleep-inducing hormones like melatonin, according to an analysis published in the journal Nutrients. And when you’re not getting good sleep, you’re more likely to end up fatigued the next day.

Can a vitamin D deficiency cause permanent damage?

In theory, yes. Severe, long-term vitamin D deficiency can cause rickets (the softening of bones in children) or osteomalacia (the softening of bones in adults). These conditions can inhibit bone growth in kids and lead to long-term bone damage or a higher risk of fractures in adults.

But in today’s world, the vast majority of people who don’t get enough D aren’t deficient enough to end up with these conditions. “Subtle deficiencies, while associated with many conditions have never been proven to directly cause or contribute to any disease,” says Dr. Cutler, who adds that fortifying foods like milk and cereal with vitamin D “has virtually eliminated rickets.”

That said, if you’re experiencing symptoms of a vitamin D deficiency, reaching out to your healthcare provider is important. They can test your vitamin D levels and recommend supplements or medications to help improve symptoms.

How to test for low vitamin D

Your healthcare provider can quickly check your vitamin D levels with a simple blood test. Vitamin D tests aren’t usually part of a routine checkup, so you’ll likely have to ask for it. However, if you’re at risk of developing a deficiency, your healthcare provider will probably recommend an annual test for you. The most common type of vitamin D blood test is the 25-hydroxyvitamin D or 25(OH)D, according to the National Library of Medicine.

It’s a good idea (for most people) to get this test when you’re undergoing routine labs. Your results can help you and your provider understand your vitamin D status and come up with a treatment plan that fits your needs. While you may be tempted to take supplements or gummies at home to combat symptoms, it’s always important to check with your healthcare team first. “No one should just take a supplement without knowing their baseline levels,” Gomer says. If you don’t know where your levels actually are, you could risk supplementing with too much and develop vitamin D toxicity (a buildup of calcium in your blood that can cause symptoms like nausea, weakness, and frequent urination), per the Mayo Clinic.

How to get more vitamin D

If you and your provider decide that you should be getting more vitamin D, you can talk about the best way to bring your levels back to where they should be. Fortunately, you’ve got a few options to get more vitamin D.

Supplements

Your provider might recommend taking a vitamin D supplement depending on how low your levels are and other factors that might influence your absorption (like your skin color, your weight, and where you live), per the Office of Dietary Supplements at the National Institutes of Health (NIH). If they do suggest a supplement, be sure to stick with their guidelines for dosing. Taking megadoses of vitamin D can be toxic, but not getting enough can exacerbate your symptoms.

Sun Exposure

The body synthesizes vitamin D from sunlight, and most of us get at least some vitamin D when our bare skin (meaning, no sunscreen) is exposed to the sun’s rays. Spending five to 30 minutes in the sun, between 10:00 a.m. and 4:00 p.m. a few times a week may be enough, notes the NIH. However, being older or having darker skin can make it harder to get enough vitamin D from the sun, so it’s important to ask your provider what you can do to get more sunlight while keeping your skin safe from harmful rays.

Food

It’s tough to get enough D from food alone, Gomer says. But you can certainly get some. According to the Office of Dietary Supplements, some of the best sources of vitamin D come from foods such as:

• Fatty fish like salmon, trout, mackerel, sardines, or tuna
• Fortified milk and cereals
• Mushrooms
• Egg yolks
• Cheese

The bottom line

Most people don’t always know that they have vitamin D levels, as signs usually don’t appear until your levels are extremely low. However, a vitamin D deficiency can cause symptoms that affect your quality of life and your overall well-being. If you’re experiencing common symptoms of low vitamin D—such as pale skin, hair loss, or changes in mood—seeing a healthcare provider is a good idea. They can order tests, help you understand your baseline, and recommend treatments to improve your symptoms.