During the winter months, many of us don’t get enough vitamin D because one of the best sources of this important vitamin is sunshine. Indeed, an estimated 42 percent of Americans are deficient in the nutrient, according to Cleveland Clinic Mercy Hospital.
Ann Louise Gittleman, PhD, author of Radical Longevity, who is based in Coeur d'Alene, Idaho, recommends people with light skin get 10 to 15 minutes of unprotected sun exposure per day to help increase their vitamin D levels. “People who tan easily can go up to 30 minutes, and people with dark skin may be able to tolerate two hours,” she says. “I'm always telling people to embrace the sun cautiously.” In smaller amounts, vitamin D exists in certain foods, such as fatty fish, fortified breakfast cereal, and mushrooms exposed to UV light, according to the National Institutes of Health (NIH).
According to the NIH’s Office of Dietary Supplements, healthy and nonpregnant adults younger than age 71 need at least 15 micrograms (mcg), which is equivalent to 600 IU of vitamin D per day — through fortified foods, sun exposure, or if needed, supplementation. Dosage recommendations can vary depending on factors such as age and life stage.
“If you’re not getting enough vitamin D from sunlight then your daily intake should be closer to 1,000 international units (IU) or 25 mcg per day,” says Shannon Henry, a registered dietitian-nutritionist with EZCareClinic in San Francisco. Before committing to any supplement long term, coordinate with your healthcare team to determine whether the supplement is a good fit for your healthcare plan. If so, they will be able to advise on the right dosage.
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Vitamin D Deficiency and Health Conditions
More studies on the role of vitamin D and health are needed. Specifically, studies looking at if taking vitamin D supplementation reduces the risk of certain diseases or ailments are lacking. Many studies have found an association, but not a cause-and-effect relationship, between people with specific diseases and having low vitamin D. What scientists are sure of, however, is that when vitamin D deficiency is severe, the risk for bone diseases such as rickets in children and osteomalacia in adults increases, per the NIH.
Below are examples of associations between low vitamin D and specific diseases:
Depression
Low vitamin D levels have been associated with depression, according to past research involving more than 31,000 study participants.
This may be because vitamin D and its receptors are found in the areas of the brain involved with mood and behavior, per a study published in May 2020 in the Journal of Affective Disorders. “Vitamin D plays an important role in healthy brain functions,” Henry says. For those with mild to moderate depression, supplementing with vitamin D may help, the study researchers wrote, though more studies are needed before vitamin D supplement prescriptions for depression are standard.
Dementia
A meta-analysis published in November 2019 in BMC Neurology found a link between vitamin D deficiency and people with dementia, including the most common type of the condition, Alzheimer’s disease. The more severe the deficiency, the stronger the association.
Prostate Cancer
Another previous study found a link between low blood levels of vitamin D and aggressive prostate cancer in European American and African American men undergoing their first prostate biopsy after being referred for an abnormal prostate-specific antigen or digital rectal examination.
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Erectile Dysfunction
A systematic review and meta-analysis published in May 2020 in Nutrients found that men with severe erectile dysfunction (ED) had lower vitamin D levels than men with mild ED.
Schizophrenia
People with schizophrenia are more likely to be deficient in vitamin D, according to a systematic review and meta-analysis published in June 2020 in Psychiatry Research. This may be because of the role vitamin D plays on the body’s inflammatory and immune responses, according to a past review.
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Symptoms of Vitamin D Deficiency
But how do you know if you’re vitamin D deficient? The best way is through a simple blood test, which your primary care physician can carry out. Ideally, your vitamin D levels will be around 20 nanograms per milliliter (ng/mL), per the NIH.
That said, certain symptoms may suggest your vitamin D levels are too low. Here are five signs to watch out for:
1. Fatigue
Feeling fatigued and sluggish is probably the most common sign of vitamin D deficiency, Dr. Gittleman says. One previous study suggested that there is a significant correlation between daytime sleepiness and low levels of vitamin D.
Vitamin D supplements may help reverse the trend: Another past study of people with fatigue and vitamin D deficiency found that vitamin D treatment improved participants’ subjective fatigue rating scale compared to the placebo group.
2. Broken Bones and Stress Fractures
“Bone fractures that don't heal quickly are another sign [of vitamin D deficiency],” Gittleman says.
That’s because one of the critical roles of vitamin D is to help the body absorb calcium, which supports bone health, according to the NIH. Research indicates that adequate vitamin D and calcium levels can promote healthy bones and help prevent osteoporosis, according to the Mayo Clinic.
A meta-analysis of randomized controlled trials published August 2020 in Medicine found that supplementing with vitamin D (specifically, vitamin D3) and calcium reduced the incidence of both falls and fractures in the study participants.
According to the National Institute on Aging, people tend to stop building bone mass around age 30, so adequate vitamin D intake is important to keep the bones in good condition as you age.
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3. Low Immunity
Another important function of vitamin D: keeping the immune system running adequately and appropriately.
Some studies have associated lower levels of vitamin D with increased risk of infection. Before antibiotics were available, vitamin D was used to treat infections like tuberculosis, per the Harvard T.H. Chan School of Public Health.
For example, a systematic review and meta-analysis published in February 2017 in the BMJ found that supplementing with vitamin D reduced participants’ risk of acute respiratory tract infection. Those with the greatest vitamin D deficiency — less than 25 nmol/L at baseline — who supplemented at least once a week or daily reduced their risk of respiratory infection by 50 percent compared with participants whose vitamin D levels were 25nnmol/L or higher.
“Quite frankly, [the link is] huge,” Gittleman says from her clinical care experiences. She notes if you seem to be catching every cold, flu, and virus that comes along, you may be deficient in vitamin D and this is something to discuss with your primary care provider. They can test your vitamin D levels and evaluate you for other potential causes that may be impeding your immune function.
Because of that link, maintaining healthy vitamin D levels may also play a protective role against COVID-19. A study published in October 2020 The Journal of Clinical Endocrinology and Metabolism found that 82 percent of the 216 COVID-19 hospitalized patients included in the study were deficient in vitamin D, though research so far hasn’t found a causal relationship.
4. Muscle Pain and Achiness
In some cases, vitamin D deficiency can cause muscle pain and achiness. As mentioned, a vitamin D status test can determine whether this vitamin deficiency is at the root of these symptoms.
If it is, your doctor may recommend a vitamin D supplement, which an article published in June 2018 in Bone Reports noted may help reduce muscle aches and pains. In other research, a review published in July 2018 in the Journal of the American Academy of Orthopaedic Surgery also found supplementing with vitamin D can increase muscle strength among those who are deficient.
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5. Hair Loss
Henry notes that alopecia, or hair loss, is also linked to low vitamin D. One past study noted a correlation between low vitamin D levels and female-pattern hair loss, which affects more than 55 percent of women over age 70. Another study, published March 2019 in Dermatology and Therapy, emphasized this link but suggested that more research is needed to determine whether vitamin D supplementation can prevent hair loss.