Vitamin D is an extremely important vitamin that has powerful effects on several systems throughout your body (1Trusted Source).
Unlike other vitamins, vitamin D 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, though it’s very difficult to get enough from diet alone.
The recommended daily intake (RDI) 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 (2Trusted Source).
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 (3Trusted Source).
Here are 7 common risk factors for vitamin D deficiency:
- Having dark skin.
- Being elderly.
- Being overweight or obese.
- Not eating much fish or dairy.
- 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, as their skin produces enough vitamin D to satisfy their bodies’ needs.
Most people don’t realize that they’re deficient, as symptoms are generally subtle. You may not recognize them easily, even if they’re having a significant negative effect on your quality of life.
Here are 8 signs and symptoms of vitamin D deficiency.
1. Getting Sick or Infected Often
One of vitamin D’s most important roles is keeping your immune system strong so you’re able to fight off viruses and bacteria that cause illness.
It directly interacts with the cells that are responsible for fighting infection (4Trusted Source).
If you often become sick, especially with colds or the flu, low vitamin D levels may be a contributing factor.
Several large observational studies have shown a link between a deficiency and respiratory tract infections like colds, bronchitis and pneumonia (5Trusted Source, 6Trusted Source).
A number of studies have found that taking vitamin D supplements at a dosage of up to 4,000 IU daily may reduce your risk of respiratory tract infections (7Trusted Source, 8Trusted Source, 9Trusted Source).
In one study in 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 (10Trusted Source).
2. Fatigue and Tiredness
Feeling tired can have many causes, and vitamin D deficiency may be one of them.
Unfortunately, it’s often overlooked as a potential cause.
Case studies have shown that very low blood levels can cause fatigue that has a severe negative effect on quality of life (11Trusted Source, 12Trusted Source).
In one case, a woman who complained of chronic daytime fatigue and headaches was found to have a vitamin D blood level of only 5.9 ng/ml. This is extremely low, as anything under 20 ng/ml is considered deficient.
When the woman took a vitamin D supplement, her level increased to 39 ng/ml and her symptoms resolved (12Trusted Source).
However, even blood levels that aren’t extremely low may have a negative impact on your 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 lower than 20 ng/ml or 21–29 ng/ml were more likely to complain of fatigue than those with blood levels over 30 ng/ml (13Trusted Source).
Another observational study in 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 (14Trusted Source).
For more information on how to reduce fatigue, consider reading about the 11 best vitamins and supplements to boost energy.
3. Bone and Back Pain
Vitamin D helps maintain bone health in a number of ways.
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.
Large observational studies have found a relationship between a deficiency and chronic lower back pain (15Trusted Source, 16Trusted Source, 17Trusted Source).
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 (17Trusted Source).
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 (18Trusted Source).
4. Depression
A depressed mood may also be a sign of vitamin D deficiency.
In review studies, researchers have linked vitamin D deficiency to depression, particularly in older adults (19Trusted Source, 20Trusted Source).
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 (19Trusted Source).
However, the researchers who analyzed the studies noted that the dosages of vitamin D in controlled studies were often very low.
In addition, they observed that some of the studies may not have lasted long enough to see the effect of taking supplements on mood.
Some controlled studies have shown that giving vitamin D to people who are deficient helps improve depression, including seasonal depression that occurs during the colder months (21Trusted Source, 22Trusted Source).
5. Impaired Wound Healing
Slow healing of wounds after surgery or injury may be a sign that your vitamin D levels are too low.
Results from a test-tube study suggest that the vitamin increases the production of compounds that are crucial for forming new skin as part of the wound-healing process (23Trusted Source).
One study on people who had dental surgery found that certain aspects of healing were compromised by vitamin D deficiency (24Trusted Source).
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 (25Trusted Source).
Unfortunately, there is very little research about the effects of vitamin D supplements on wound healing in people with deficiency at this point.
However, one study found that when vitamin D deficient patients with leg ulcers were treated with the vitamin, ulcer size reduced by on 28%, on average (26Trusted Source).
6. Bone Loss
Vitamin D plays a crucial role in calcium absorption and bone metabolism.
Many older people 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 your bones have lost calcium and other minerals. This places older adults, especially women, at an increased risk of fractures.
In a large observational study in 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 (27Trusted Source).
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 (28Trusted Source).
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.