The only way to know for sure if you’re vitamin D deficient is via blood testing. However, there are some signs and symptoms to be aware of as well. If any of the following apply to you, you should get your vitamin D levels tested sooner rather than later.
1. You Have Darker Skin
Your skin pigment acts as a natural sunscreen, so the more pigment you have, the more time you’ll need to spend in the sun to make adequate amounts of vitamin D.
2. You Feel “Blue”
Serotonin, the brain hormone associated with mood elevation, rises with exposure to bright light and falls with decreased sun exposure.
3. You’re 50 or Older
As mentioned, as you get older your skin doesn’t make as much vitamin D in response to sun exposure.
4. You’re Overweight or Obese (or Have a Higher Muscle Mass)
Vitamin D is a fat-soluble, hormone-like vitamin, which means body fat acts as a "sink" by collecting it. If you're overweight or obese, you're therefore likely going to need more vitamin D than a slimmer person -- and the same holds true for people with higher body weights due to muscle mass.
5. Your Bones Ache
According to Dr.Alpa, many who see their doctor for aches and pains, especially in combination with fatigue, end up being misdiagnosed as having fibromyalgia or chronic fatigue syndrome.
6. Head Sweating
According to Dr. Alpa, one of the first, classic signs of vitamin D deficiency is a sweaty head
7. You Have Gut Trouble
Remember, vitamin D is a fat-soluble vitamin, which means if you have a gastrointestinal condition that affects your ability to absorb fat, you may have lower absorption of fat-soluble vitamins like vitamin D as well. This includes gut conditions like Crohn’s, celiac and non-celiac gluten sensitivity, and inflammatory bowel disease.