Did you know that before the year 2000, most doctors believed that none of their patients could be vitamin D deficient? But as technology to measure for vitamin D became affordable, more studies were conducted. According to Dr. Michael Holick, who is one of the leading vitamin D researchers, The Centers for Disease Control and Prevention (CDC) reported that 32% of adults and children in the US were vitamin D deficient. That’s a pretty high number; so for that reason alone, it’s important that you look for signs of vitamin D deficiency.

With more research being conducted, Holick believes that about 50% of the general population may be at risk of vitamin D deficiency.

The only way to know for sure if you are vitamin D deficient is by a blood test. But the signs and symptoms that come along with this deficiency could be helpful as well. If any of the following signs apply to you, it might be a good idea to go see your doctor and have your blood checked, because you might be vitamin D deficient.

Darker Skin: Holick explains that if you have darker skin, you may need as much as 10 times more sun exposure to get the same amount of vitamin D as an individual with pale skin. He adds that your skin pigment acts as a natural sunscreen, so the more pigment you have, the more time you need to spend in the sun.

You Have the Blues: According to a study published in The American Journal of Geriatric Psychiatry, one of the signs of vitamin D deficiency is having a low mood. To prove this theory, researchers studied 80 elderly patients and they found that those who had the lowest vitamin D levels were 11 times more likely to be depressed than those who had healthy levels of vitamin D.

You’re At Least 50: According to the International Society for Clinical Densitometry, about 95% of senior citizens may be vitamin D deficient. The reason is not just because they spend a lot of their times indoors; another reason is that they produce less when they’re exposed to the sun. They add that an elderly individual over the age of 70 produces 30% less vitamin D than a younger person with the same sun exposure.

Obese, Overweight or High Muscle Mass: Holick explains that vitamin D is fat-soluble, which means that the body will collect it. So, if you are overweight or obese, your body will need a lot more vitamin D than the average person. The same goes for those who have a lot of muscle and body mass, he adds.

Aching Bones: Holick says that many patients who visit their doctor and complain about aching bones and muscles are misdiagnosed with fibromyalgia or chronic fatigue syndrome. It’s not an uncommon mistake, but what I recommend is that before the doctor diagnoses you, ask for a vitamin D blood test just so you can rule it out if it comes back negative.

Sweaty Head: According to Holick, a sweaty head is one of the first signs of vitamin D deficiency. He adds that many physicians used to ask new mothers if their newborn child was experiencing a sweaty head. Excessive sweating in newborns that’s due to neuromuscular irritability is still described as an early symptom of vitamin D deficiency.

Gut Issues: As mentioned earlier, vitamin D is fat-soluble, so if you are having gastrointestinal issues that affect your body’s ability to store fat, you could have lower absorption of fat-soluble vitamins such as vitamin D, says Holick. Certain gut conditions that are common include Crohn’s, celiac and non-celiac gluten sensitivity, and inflammatory bowel disease.

Sources of Vitamin D: According to the Dietitians of Canada, the following are great sources of vitamin D: grain products, orange juice, plain yogurt, deli meat, pork, beef liver, salmon, eggs, and fruits and vegetables. Just remember, if you experience any of the symptoms mentioned, go consult your doctor, because you may be vitamin D deficient.