Vitamin D is often associated only with strong bones, but it plays a much wider role in maintaining one’s overall wellness. Vitamin D receptors are located in cells throughout the body including the skin, brain, heart, breast, prostate gland and cells of the immune system.

According to a report published in the Archives of Internal Medicine, 77% of Americans have a deficiency in vitamin D levels, affecting their overall health.

Vitamin D from Sunlight

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The main natural source of vitamin D for humans comes from adequate amounts of sunlight exposure.

Short wave ultraviolet B (UVB) rays from the sun convert a substance in the skin called 7-dehydrocholesterol into vitamin D. Anything that interferes with the penetration of UVB radiation into the skin will affect the synthesis of vitamin D..

Melanin, which creates skin pigmentation absorbs UVB radiation, so darker-skinned people in northern climates are more likely to be vitamin D deficient.

Sunscreen with SPF 15 decreases the synthesis of vitamin D by 99% when applied properly. The amount of sun exposure you need to get adequate vitamin D depends on your skin type, your location, season of the year and time of day.

Vitamin D from Food Sources

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Food sources of vitamin D include oily fish, egg yolks and beef liver. However, these may give you less than you think.

One study found that wild-caught salmon had 500–1000 IU vitamin D in 100 grams, while farmed salmon (the most widely consumed fish in the US) contained only 100-250 IU per 100 grams.

According to the NIH, the recommended dietary allowance (RDA) for vitamin D is 600 IU per day. Most people get far less than this on a daily basis. The National Health and Nutrition Examination Survey estimated the average vitamin D intake from food alone ranged from 204-288 IU per day for males and 144-276 IU for females.

8 Science-Backed Health Benefits of Vitamin D

1. Prevents Osteoporosis

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Calcium is the most important mineral for building strong bones. Our bodies continuously removes calcium from our bones and replace it with new calcium from our diet.

Vitamin D plays a vital role in helping our bodies absorb calcium from food. If you don’t get enough calcium and vitamin D, you have a greater risk of developing osteoporosis, especially for post-menopausal woman.

Osteoporosis causes bones to become less dense and more likely to break after a fall or minor accident. In addition to building strong bones, vitamin D helps to prevent falls by improving muscle function in the legs.

A year-long trial in Scotland examined the effect of vitamin D supplementation on bone mineral density. A total of 305 healthy women aged 60-70 were randomized to receive either a daily 400 IU vitamin D supplement, a 1000 IU vitamin D supplement or a placebo. At the beginning and end of the study, the participants had scans and blood tests to determine bone mineral density of the hip and spine.

After one year, bone loss at the hip was significantly greater for the placebo and 400 IU vitamin D groups compared with the 1,000 IU vitamin D group. Bone loss was negligible for women on the higher dose of vitamin D.

A meta-analysis of randomized controlled trials examined the efficacy of vitamin D supplements for preventing non-vertebral and hip fractures among adults aged over 65. Researchers analyzed data from 12 trials for non-vertebral fractures and 8 trials for hip fractures comparing oral vitamin D with calcium and/or a placebo. They grouped the trials by low dose (less than 400 IU of vitamin D per day) or higher dose.

Analysis of the data showed that a higher dose of vitamin D (482-770 IU per day) reduced non-vertebral fractures by at least 20% and hip fractures by at least 18%. The lower dose had no significant effect.

A pooled analysis published in the New England Journal of Medicine examined the dose requirements of vitamin D for the prevention of bone fractures. Researchers combined data from 11 double-blind, randomized, controlled trials of vitamin D supplementation involving a total of 31,022 participants with 1,111 incidents of hip fracture and 3,770 other non-vertebral fractures.

Low doses of vitamin D supplements did not significantly reduce the risk for fractures. However, doses ranging from 792-2,000 IU daily reduced the risk of hip fracture by 30% and the risk of other non-vertebral fractures by 14%.

A clinical trial published in the Journal of the American Geriatrics Society set out to determine the effect of 4 vitamin D supplement doses on the risk of falls in elderly nursing home residents. A total of 124 nursing home residents were randomly assigned to receive 200 IU, 400 IU, 600 IU, or 800 IU of vitamin D or a placebo daily for 5 months.

The 800 IU vitamin D group had a significantly reduced number of fallers and a reduced incidence rate of falls compared to those taking lower doses or a placebo. The high dose of vitamin D reduced the risk of falling by 72%. Lower doses were not significantly more effective than the placebo.


2. Treats Depression

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Vitamin D receptors are found in the areas of the brain, such as the hippocampus, that are linked to the development of depression.

While the role of vitamin D in the brain isn’t fully understood, some researchers theorize that it may increase levels of serotonin and other neurotransmitters involved in regulating mood.

A study published in the British Journal of Nutrition investigated the relationship of vitamin D with the prevalence of depressive and anxiety disorders. Researchers analyzed data from 5,371 men and women involved in a Finnish health survey. The participants included 354 people who have been diagnosed with depression. Blood samples were used to measure vitamin D concentrations for all subjects.

Those with the highest levels of vitamin D had a 35% lower risk of depressive disorder than those with the lowest levels. The protective effect of vitamin D remained even after adjustment for depression risk factors such as divorce, illness or unhealthy lifestyle.

A Turkish study investigated the link between mid-pregnancy vitamin D levels and postpartum depression. Study participants included 179 women with no known risk factors for postpartum depression. They were screened for vitamin D levels when they were 24 – 28 weeks pregnant.

At one week, 6 weeks and 6 months after delivery, participants were assessed using the Edinburgh Postnatal Depression Scale (EPDS). There was a significant relationship between low vitamin D levels in mid-pregnancy and high EPDS scores in all 3 follow-up periods.

A randomized controlled trial published in the Journal of Internal Medicine examined the effects of vitamin D supplementation on symptoms of depression in overweight and obese subjects. Researchers recruited 441 men and women with a BMI over 27.

All of the subjects completed a standard questionnaire called the Beck Depression Inventory at the start and end of the study. They also took blood tests to determine their levels of vitamin D. The participants were randomized to receive 1 of 3 treatments: 2 capsules of vitamin D, 1 capsule of vitamin D and 1 placebo capsule, or 2 placebo capsules.

At the start of the study, participants with low vitamin D levels scored significantly higher for depressive traits than those with higher vitamin D levels. After 1 year of supplementation, subjects in the 2 groups given vitamin D showed a significant improvement in depression scores, whereas those in the placebo group did not improve.

A meta-analysis published in Psychosomatic Medicine reviewed the effects of vitamin D supplementation on depression in 7 randomized controlled trials. Researchers concluded that vitamin D supplementation had a moderate, statistically significant effect on depressive symptoms for patients with clinically significant depressive symptoms or depressive disorder.


3. Boosts Our Immune System

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The peak of the flu season occurs in the winter, when vitamin D levels in the population are at their lowest.

A study which analyzed data from the 1,918-1,919 influenza pandemic found that the lowest flu-related death rates in the US were in southern cities with the highest amounts of UVB light. The most flu fatalities were in northern cities with the lowest amounts of UVB radiation.

Vitamin D helps to boost the immune system and protect against colds and flu in two ways. It modulates the production of inflammatory proteins called cytokines and stimulates production of antimicrobial proteins that fight viral infections.

A prospective study was conducted in Greenwich, Connecticut to determine whether the incidence of acute viral respiratory tract infections was associated with vitamin D levels. Researchers recruited 198 healthy adults who volunteered to have their blood drawn monthly from September to January. They were also asked to report any cold or flu symptoms they experienced over this period.

Participants’ blood samples were tested for vitamin D levels. Those who reported symptoms had nasal swabs tested for the presence of a viral respiratory tract infection. Analysis of the data showed that the higher the vitamin D concentrations in the blood, the lower that risk for colds or flu. Participants with low levels of vitamin D were twice as likely to develop a viral respiratory tract infection than those with higher levels.

When researchers at the Winthrop University Hospital conducted a trial to determine whether vitamin D would prevent osteoporosis, they came up with an unexpected result. Researchers randomized 208 African-American postmenopausal women to receive either a placebo or 800 IU vitamin D per day for 2 years followed by 2,000 IU per day for a third year.

Patients were followed up every 6 months to have their bone mineral density measured. During these visits, they were asked about their overall health including incidence of cold or flu.

In a report published in Epidemiology and Infection, the researchers noted that 8 women in the vitamin D group experienced cold or flu symptoms compared with 26 women in the placebo group. Only one subject in the vitamin D group experienced cold or flu symptoms while on the higher dose.

A controlled trial published in the American Journal of Clinical Nutrition investigated the effect of vitamin D supplements on seasonal influenza in children. A total of 430 Japanese school children were randomly assigned to receive tablets containing 1,200 IU of vitamin D per day or placebo tablets during the flu season from December to March.

In the vitamin D group, 11% of children developed influenza type A (bird flu) compared with 19% in the placebo group. Vitamin D reduced the risk for this type of viral infection by 42% for all participants. For those who had not been taking vitamin D prior to the study, the risk was reduced by 64%. Vitamin D supplements also protected against asthma attacks in children previously diagnosed with asthma.


4. Prevents Alzheimer’s Disease & Dementia

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Several population studies have shown that people who are deficient in vitamin D are at greater risk for developing Alzheimer’s disease and dementia.

The cognitive changes, such as memory loss, that take place in Alzheimer’s disease occur when amyloid-beta protein fragments accumulate in the brain to form insoluble plaques.

Laboratory research has shown that vitamin D helps the immune system to clear excess amyloid-beta and inhibits brain cell death induced by amyloid-beta.

A Danish population study published in Alzheimer’s and Dementia investigated the association between vitamin D levels and risk of developing Alzheimer’s. Researchers measured blood levels of vitamin D in a cohort of 10,186 adults who were free of any type of diagnosed dementia.

During 30 years of follow-up, 418 participants developed Alzheimer’s and 92 developed vascular dementia. After adjusting for other risk factors such as high cholesterol and obesity, the researchers observed an association between low vitamin D levels with a significantly increased risk of Alzheimer’s disease and vascular dementia.

A study published in Dementia and Geriatric Cognitive Disorders examined the association between vitamin D status and cognition in 225 patients who were diagnosed as having probable Alzheimer’s disease.

The patients were tested on the Mini-Mental State Examination (MMSE), a common diagnostic tool used to measure cognitive impairment and screen for dementia. Their blood samples were tested to determine vitamin D levels. Analysis of the data showed that patients with sufficient vitamin D levels scored significantly better on the MMSE than vitamin D insufficient patients.

A study at the University of California at Davis Alzheimer’s Disease Center assessed associations between vitamin D status and cognitive function. A cohort of 382 ethnically diverse adults over age 60 were clinically assessed for cognitive impairment or dementia.

Their blood levels of vitamin D were measured and categorized as deficient, insufficient, adequate or high.

At the time of enrollment in the study, 18% of participants were diagnosed with dementia, 33% had mild cognitive impairment and 50% were cognitively normal. Average vitamin D levels were significantly lower in participants with dementia.

After 5 years of follow-up, rates of decline in episodic memory and executive function were significantly higher in participants with deficient or insufficient vitamin D. Vitamin D insufficiency was associated with a level of decline in episodic memory performance that was 3 times greater than in individuals who remained cognitively normal.


5. Protects Against Breast Cancer

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Breast cells are capable of converting vitamin D to a hormone which has anti-carcinogenic properties.

Laboratory research has shown that the hormonally active form of vitamin D inhibits the proliferation and spread of cancer cells and stimulates cancer cell death. Having sufficient vitamin D from sun exposure, diet or supplements lowers the risk for developing breast cancer and can increase survival rates for breast cancer patients.

A meta-analysis published in Medicine evaluated the association between circulating vitamin D and breast cancer risk. Researchers pooled data from 9 prospective studies, comprising of 5,206 cancer cases and 6,450 controls. They found that for post-menopausal women, the higher their vitamin D levels, the lower their risk for breast cancer.

A population-based study conducted in Ontario, Canada investigated the association between sunlight exposure and risk of breast cancer. Researchers recruited 3,101 women aged 25–74 who had been diagnosed with breast cancer and 3,471 healthy age-matched controls. The participants filled in breast cancer risk factor questionnaires that included questions about hours per day spent outdoors in the months of April–October.

The researchers compared women with the highest sun exposure to those with the lowest sun exposure during 4 life periods. Those who spent the most time outdoors during their teenage years had a 21% lower risk of breast cancer. Sun exposure reduced the risk of cancer by 24% for women in their 20s-30s and by 25% for women in their 40s-50s. Older women aged 60-75 benefited the most from time spent outdoors, with a 41% reduction in breast cancer risk.

A 4-year trial published in the American Journal of Clinical Nutrition examined the efficacy of calcium alone and calcium plus vitamin D in reducing the risk of all types of cancer. A total of 1,179 healthy Nebraskan woman aged 55 and older were randomly assigned to 3 groups. One group received placebo supplements, one group received 1,450 mg calcium supplements and one group received calcium plus 1,100 IU per day of vitamin D. The risk of developing any type of cancer after the first year of the trial was reduced by 77% for women taking calcium and vitamin D. Calcium alone reduced the risk for cancer by 41% compared to the placebo.

A Korean study investigated the association between vitamin D status and the prognosis of breast cancer patients. Researchers tested blood concentrations of vitamin D for 469 breast cancer patients at diagnosis and categorized them as deficient or non-deficient. The patients had their vitamin D levels tested again at annual follow-up visits for up to 4 years after diagnosis.

Patients aged over 55 and those with advanced-stage cancer who were non-deficient in vitamin D had a significantly better survival rate compared to those with vitamin D deficiency. At the one-year follow up, patients who remained non-deficient and those whose vitamin D levels had improved were also more likely to survive over the course of the study.


6. Protects Against Prostate Cancer

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Vitamin D appears to have a protective effect against prostate cancer. Population studies have shown that prostate cancer is most common in Northern climates with less UV light than southern climates.

In the US, African-American men, whose dark skin does not absorb as much UV radiation, are 2 times more likely to die from prostate cancer than Caucasian men.

Laboratory research has shown that cells in the prostate can convert circulating vitamin D to an active hormone. This hormonal form of vitamin D inhibits the growth and spread of cancer cells.

A prospective study investigated the association between vitamin D status and prostate cancer risk. Researchers at Harvard Medical School analyzed 18 years of data from the Physicians’ Health Study. They compared pre-diagnostic levels of vitamin D in 1,066 men who later went on to develop prostate cancer with the vitamin D levels of 1,618 cancer-free controls matched for age and smoking status. Men whose vitamin D levels were below average had a significantly increased risk of developing aggressive prostate cancer.

About 14% of men of European decent carry a genotype that makes them more prone to develop prostate cancer. The researchers found that vitamin D interacted with this genotype to modify cancer risk. Low vitamin D levels increased the genetic risk for cancer. For men with above average levels of vitamin D, the genotype was no longer associated with any increased risk.

A study published in Clinical Cancer Research evaluated the association between vitamin D and prostate biopsy outcomes. Researchers in measured the vitamin D levels of 667 men in Chicago urology clinics who were undergoing their first prostate biopsy due to an elevated prostate-specific antigen level or an abnormal digital rectal examination. Biopsies remove a small portion of tissue to check for cancerous cells.

For African American men, vitamin D deficiency was significantly associated with increased odds of prostate cancer diagnosis. Among all men who were diagnosed with prostate cancer following the biopsy, severe vitamin D deficiency was positively associated with more advanced staged tumors and higher risk categories.

A clinical trial held in Charleston, South Carolina investigated the effects of vitamin D supplementation in 44 low-risk prostate cancer patients. The participants all received daily 4,000 IU vitamin D supplements. Biopsy procedures were performed before enrollment in the study and after one year of supplementation.

At the second biopsy, 55% of patients had a decrease in cancerous cells or were in a lower cancer risk category. Compared to similar patients in a medical database who had not taken vitamin D, the supplemented patients had a lower rate of cancer progression and a significantly higher rate of improvement.

The researchers note that a combination of active surveillance and vitamin D supplementation may decrease the need of invasive treatments, such as surgery or radiation therapy, for patients with low-risk prostate cancer who respond to the treatment and remain stable or improve.


7. Fights Inflammatory Bowel Disease

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Research suggests that vitamin D may fight against many immune system disruptions that occur in inflammatory bowel disease.

Vitamin D protects the epithelial lining of the gastrointestinal tract which forms a barrier against pathogens and induces the production of antibacterial enzymes. It also maintains immune tolerance and reduces inflammation.

A study published in Digestive Diseases and Sciences examined the relationship between vitamin D levels and clinical disease activity in patients with ulcerative colitis. Researchers at the Hospital of the University of Pennsylvania went through medical records and identified patients with a diagnosis of ulcerative colitis who had been tested for vitamin D status.

They found 15 ulcerative colitis patients with normal vitamin D levels and 19 who were vitamin D deficient. Patients with low vitamin D levels were statistically more likely to have increased disease activity, with 68% of deficient patients displaying active disease, compared with 33% in the vitamin D sufficient group. Among the deficient patients, 47% were treated with corticosteroids, whereas only 7% of the vitamin D sufficient patients required such treatment.

A pilot study published in Clinical and Translational Gastroenterology examined the effect of vitamin D supplementation on 18 patients with mild-to-moderate Crohn’s disease. The participants took 1,000 IU of vitamin D per day for 2 weeks. The dose was raised incrementally until the patients’ vitamin D levels were optimal or until they were taking 5,000 IU per day. Patients were evaluated for severity of symptoms using the Crohn’s disease activity index (CDAI) at the beginning and end of the 24-week study.

Vitamin D supplementation significantly reduced overall CDAI scores, and all but one patient had a lower CDAI score. The scores indicated that 67% of the patients were in remission at the end of the study. Quality-of-life scores also significantly improved.

A clinical trial published in Alimentary Pharmacology and Therapeutics assessed the effectiveness of vitamin D3 treatment in Crohn’s disease. A total of 94 patients with Crohn’s disease in remission were randomized to receive either 1,200 IU vitamin D per day or a placebo.

After 12 months, the relapse rate for patients in the vitamin D group was 13%, less than half the 29% relapse rate for the placebo group. The researchers suggest that vitamin D treatment may potentially reduce the use of remission-inducing drugs such as corticosteroids.


8. Lowers Blood Sugar for Type 2 Diabetes

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Beta cells in your pancreas produce the hormone, insulin, which regulates blood sugar. Type 2 diabetes occurs when beta cells do not produce enough insulin or when cells in the body become insulin resistant, resulting in dangerously high blood sugar levels.

Vitamin D seems to play a role in pancreatic beta cell function. Research on mice has shown that removing vitamin D receptors from beta cells decreases insulin production by up to 60%.

A meta-analysis published in Diabetes Care assessed the strength of the association between vitamin D levels and risk of type 2 diabetes. Researchers analyzed data from of 21 prospective studies involving 76,220 participants and 4,996 cases of type 2 diabetes.

The analysis revealed a trend where the higher the vitamin D levels, the lower the risk of type 2 diabetes. Participants with the highest blood levels of vitamin D were 38% less likely to develop type 2 diabetes compared to participants with the lowest levels.

A controlled trial published in the American Journal of Clinical Nutrition investigated the effects of vitamin D supplementation on metabolic health factors related to obesity. Researchers recruited 35 patients aged 14-16 from an adolescent diabetes and obesity clinic. The participants were randomly assigned to receive either a daily 4,000 IU vitamin D supplement or a placebo.

After 6 months, the vitamin D group showed significant improvement in 3 blood markers for insulin resistance and insulin sensitivity. Researchers concluded that vitamin D supplementation helped to repair the damaged blood sugar metabolism associated with obesity.

A randomized controlled trial examined the effects of vitamin D and calcium supplementation on blood sugar metabolism in adults with a high risk of diabetes. A total of 92 participants were given daily supplements containing either 2,000 IU of vitamin D, 400 mg of calcium or a placebo. At the start and end of the trial, participants underwent an intravenous-glucose-tolerance test.

After 16 weeks, those in the vitamin D group showed a significant improvement in insulin production and secretion from pancreatic beta cells. The calcium group showed no significant difference in insulin response.

An Iranian trial tested the effects of a vitamin D fortified yogurt drink on patients with type 2 diabetes. A total of 100 diabetic men and women were randomly allocated to receive either plain yogurt drinks or yogurt drinks containing 500 IU of vitamin D and 170 mg calcium. They consumed 2 drinks a day with lunch and dinner. Blood tests were performed before and after the trial.

After 12 weeks, the group who drank vitamin D fortified yogurt had significantly lower blood sugar levels and increased glucose regulation compared to the plain yogurt group. They also had less vascular inflammation, lower LDL ‘bad’ cholesterol and higher HDL ‘good’ cholesterol.


Final Word

The only way to know whether you’re getting sufficient vitamin D is to take a 25(OH)D blood test. You can ask your doctor for this test or you can order an in-home test online.

With the in-home test, you prick your finger and send a small blood sample to a laboratory. Your results will usually be available within 2 weeks.

The Endocrine Society clinical practice guidelines for vitamin D state that the desirable blood concentration is 30 ng/ml or greater. They also report that adults may require at least 1,500-2,000 IU per day of vitamin D supplements to consistently reach this level.

If you live in a climate with dark winter days, or spend most of the day indoors, vitamin D supplements may improve your health in a variety of ways.

Rebecca Park has a degree in Nursing, Speech Pathology & Audiology. She currently lives in New York City, where she was born and raised. She enjoys traveling all over the world with her husband and son to learn about different cultures and their healthcare. As a practicing Registered Nurse, Rebecca likes to explore natural remedies and alternative methods to complement modern medicine to treat people as a whole and not just their symptoms.


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