Vitamin D is an extremely important vitamin that has powerful effects on several systems throughout the body (1).
Unlike most vitamins, vitamin D actually functions like a hormone, and every single cell in your body has a receptor for it.
Your body makes it from cholesterol when your skin is exposed to sunlight.
It's also found in certain foods such as fatty fish and fortified dairy products, although it's very difficult to get enough from diet alone.
The recommended daily intake is usually around 400-800 IU, but many experts say you should get even more than that.
Vitamin D deficiency is very common. It's estimated that about 1 billion people worldwide have low levels of the vitamin in their blood (2).
According to a 2011 study, 41.6% of adults in the US are deficient. This number goes up to 69.2% in Hispanics and 82.1% in African-Americans (3).
These are common risk factors for vitamin D deficiency:
- Having dark skin.
- Being elderly.
- Being overweight or obese.
- Not eating much fish or milk.
- Living far from the equator where there is little sun year-round.
- Always using sunscreen when going out.
- Staying indoors.
People who live near the equator and get frequent sun exposure are less likely to be deficient, because their skin produces enough vitamin D to satisfy the body's needs.
Most people don't realize that they are deficient, because the symptoms are generally subtle. You may not notice them easily, even if they are having a significant negative effect on your quality of life.
Here are 8 signs and symptoms of vitamin D deficiency.
One of vitamin D's most important roles is keeping your immune system strong so you're able to fight off the viruses and bacteria that cause illness.
It directly interacts with the cells that are responsible for fighting infection (4).
If you become sick often, especially with colds or the flu, low vitamin D levels may be a contributing factor.
In one study of people with the chronic lung disorder COPD, only those who were severely deficient in vitamin D experienced a significant benefit after taking a high-dose supplement for one year (10).
Bottom Line: Vitamin D plays important roles in immune function. One of the most common symptoms of deficiency is an increased risk of illness or infections.
Feeling tired can have many causes and vitamin D deficiency may be one of them.
Unfortunately, it's often overlooked as a potential cause.
In one case, a woman who complained of chronic daytime fatigue and headaches was found to have a blood level of only 5.9 ng/ml. This is extremely low, as anything under 20 ng/ml is considered to be deficient.
When the woman took a vitamin D supplement, her level increased to 39 ng/ml and her symptoms resolved (12).
However, even blood levels that aren't extremely low may have a negative impact on energy levels.
A large observational study looked at the relationship between vitamin D and fatigue in young women.
The study found that women with blood levels under 20 ng/ml or 21–29 ng/ml were more likely to complain of fatigue than those with blood levels over 30 ng/ml (13).
Another observational study of female nurses found a strong connection between low vitamin D levels and self-reported fatigue.
What's more, the researchers found that 89% of the nurses were deficient (14).
Bottom Line: Excessive fatigue and tiredness may be a sign of vitamin D deficiency. Taking supplements may help improve energy levels.
Vitamin D is involved in maintaining bone health through a number of mechanisms.
For one, it improves your body's absorption of calcium.
Bone pain and lower back pain may be signs of inadequate vitamin D levels in the blood.
One study examined the association between vitamin D levels and back pain in more than 9,000 older women.
The researchers found that those with a deficiency were more likely to have back pain, including severe back pain that limited their daily activities (17).
In one controlled study, people with vitamin D deficiency were nearly twice as likely to experience bone pain in their legs, ribs or joints compared to those with blood levels in the normal range (18).
Bottom Line: Low blood levels of the vitamin may be a cause or contributing factor to bone pain and lower back pain.
A depressed mood may also be a sign of deficiency.
In one analysis, 65% of the observational studies found a relationship between low blood levels and depression.
On the other hand, most of the controlled trials, which carry more scientific weight than observational studies, didn't show a link between the two (19).
However, the researchers who analyzed the studies noted that the dosages of vitamin D in controlled studies were often very low.
In addition, they noted that some of the studies may not have lasted long enough to see the effect of taking supplements on mood.
Bottom Line: Depression is associated with low vitamin D levels and some studies have found that supplementing improves mood.
Slow healing of wounds after surgery or injury may be a sign that vitamin D levels are too low.
Results from a test-tube study suggest that the vitamin increases production of compounds that are crucial for forming new skin as part of the wound-healing process (23).
One study on patients who had dental surgery found that certain aspects of healing were compromised by vitamin D deficiency (24).
It's also been suggested that vitamin D's role in controlling inflammation and fighting infection is important for proper healing.
One analysis looked at patients with diabetic foot infections.
It found that those with severe vitamin D deficiency were more likely to have higher levels of inflammatory markers that can jeopardize healing (25).
Unfortunately, at this point there is very little research about the effects of vitamin D supplements on wound healing in people with deficiency.
However, one study found that when vitamin D deficient patients with leg ulcers were treated with the vitamin, ulcer size reduced by 28%, on average (26).
Bottom Line: Inadequate vitamin D levels may lead to poor wound healing following surgery, injury or infection.
Vitamin D plays a crucial role in calcium absorption and bone metabolism.
Many older women who are diagnosed with bone loss believe they need to take more calcium. However, they may be deficient in vitamin D as well.
Low bone mineral density is an indication that calcium and other minerals have been lost from bone. This places older people, especially women, at an increased risk of fractures.
In a large observational study of more than 1,100 middle-aged women in menopause or postmenopause, researchers found a strong link between low vitamin D levels and low bone mineral density (27).
However, a controlled study found that women who were vitamin D deficient experienced no improvement in bone mineral density when they took high-dose supplements, even if their blood levels improved (28).
Regardless of these findings, adequate vitamin D intake and maintaining blood levels within the optimal range may be a good strategy for protecting bone mass and reducing fracture risk.
Bottom Line: A diagnosis of low bone mineral density may be a sign of vitamin D deficiency. Getting enough of this vitamin is important for preserving bone mass as you get older.
Hair loss is often attributed to stress, which is certainly a common cause.
However, when hair loss is severe, it may be the result of a disease or nutrient deficiency.
Hair loss in women has been linked to low vitamin D levels, although there is very little research on this so far (29).Alopecia areata is an autoimmune disease characterized by severe hair loss from the head and other parts of the body. It's associated with rickets, which is a disease that causes soft bones in children due to vitamin D deficiency (30).
One study in people with alopecia areata showed that lower blood levels tended to be associated with a more severe hair loss (33).
In a case study, topical application of a synthetic form of the vitamin was found to successfully treat hair loss in a young boy with a defect in the vitamin D receptor (34).
Bottom Line: Hair loss may be a sign of vitamin D deficiency in female-pattern hair loss or the autoimmune condition alopecia areata.
The causes of muscle pain are often difficult to pinpoint.
In one study, 71% of people with chronic pain were found to be deficient (37).
The vitamin D receptor is present in nerve cells called nociceptors, which sense pain.
One study in rats showed that a deficiency led to pain and sensitivity due to stimulation of nociceptors in muscles (38).
One study in 120 children with vitamin D deficiency who had growing pains found that a single dose of the vitamin reduced pain scores by an average of 57% (40).
Bottom Line: There is a link between chronic pain and low blood levels of the vitamin, which may be due to the interaction between the vitamin and pain-sensing nerve cells.
Vitamin D deficiency is incredibly common and most people are unaware of it.
That's because the symptoms are often subtle and non-specific, meaning that it's hard to know if they're caused by low vitamin D levels or something else.
If you think you may have a deficiency, then it's important that you speak to your doctor and get your blood levels measured.
Fortunately, a vitamin D deficiency is usually easy to fix. You can either increase your sun exposure, eat more vitamin D rich foods or simply take a supplement.
Fixing your deficiency is simple, easy and can have big benefits for your health.