Vitamin D Deficiency

  • Author:
    Betty Kovacs Harbolic, MS, RD

    Betty is a Registered Dietitian who earned her B.S. degree in Food and Nutrition from Marymount College of Fordham University and her M.S. degree in Clinical Nutrition from New York University. She is the Co-Director and Director of nutrition for the New York Obesity Research Center Weight Loss Program.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Vitamin D stamp on image with the sun, a jug, and glass of milk on the grass with daisies.

What is vitamin D?

The "sunshine" vitamin is a hot topic. You may have recently found out that you are deficient or know someone who is. It's shocking for most people when they have never had a problem before and believe nothing has changed to make it a problem now. The truth is that a lot has changed, and vitamin D deficiency and insufficiency is now a global public-health problem affecting an estimated 1 billion people worldwide.

The most well-known consequences to not having enough vitamin D are rickets in children and osteomalacia in adults. These are far from the only problems associated with a vitamin D deficiency. The consequences are numerous and include skeletal diseases, metabolic disorders, cancer, cardiovascular disease, autoimmune diseases, infections, cognitive disorders, and/or mortality. The majority of our knowledge about vitamin D has been discovered over the past 15 years, and with the growing issue of deficiencies, more health connections with vitamin D levels are being made. Correcting vitamin D deficiency is not as simple as taking a pill or getting more sun. This article will teach you all that you need to know about the benefits of achieving and maintaining optimal vitamin D levels.

Vitamins are considered essential nutrients because either your body cannot make them or they are made in an inadequate amount. This means you must provide them through your diet or by taking a supplement. They are essential for your health, and when you are lacking in them, there may be health consequences and diseases.

Vitamin D is one of the four fat-soluble vitamins (A, D, E, and K). There are two forms of vitamin D, D2 and D3. Vitamin D2, also known as ergocalciferol, comes from fortified foods, plant foods, and supplements. Vitamin D3, also known as cholecalciferol, comes from fortified foods, animal foods (fatty fish, cod liver oil, eggs, and liver), supplements, and can be made internally when your skin is exposed to ultraviolet (UV) radiation from the sun. Structurally, these two are not the same.

Quick GuideVitamin D Deficiency: How Much Vitamin D Is Enough?

Vitamin D Deficiency: How Much Vitamin D Is Enough?
Learn about symptoms and signs of vitamin D deficiency.

Symptoms of Vitamin D Deficiency

Does vitamin D deficiency cause symptoms?

Yes, deficiency of vitamin D can cause bone pain and muscle weakness. However, mild vitamin D deficiency is not necessarily associated with any symptoms. Vitamin D has been referred to as the "sunlight vitamin" because it is made in our skin when we are exposed to sunlight.

Vitamin D gel tablets state the recommended dietary allowance (RDA).

What are the vitamin D requirements?

There are currently two sets of guidelines for vitamin D intake. Typically, vitamin guidelines are established by the Institute of Medicine (IOM) in the form of recommended dietary allowances (RDA) or adequate intakes (AI). The RDA is the average daily intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy individuals. The Endocrine Society put together a task force to review the research and come up with a set of guidelines for "people who are at risk for deficiency." The two recommendations are as follows:

  1 to 18 years old 19 to 70 years old 71+ years old
IOM 600 IU/day 600 IU/day 800 IU/day
Endocrine Society 600-1,000 IU/day 1,500-2,000 IU/day 1,500-2,000 IU/day
An illustration depicts normal standing posture and osteoporosis.

What does vitamin D do for your health? What are symptoms and signs of vitamin D deficiency?

By the turn of the 20th century, 90% of the children living in New York, Boston, and Leyden in the Netherlands were afflicted with rickets, a bone-deforming disease. The first observation of this disease was in the mid-1600s by Whistler and Glissen, who reported that children living in industrialized cities in Great Britain had short stature and deformities of the skeleton, especially of the lower legs. It wasn't until 1889 that the discovery that "sunbathing" was important for preventing rickets came about.

Since then, many other health benefits of vitamin D have been discovered. These include the following:

Skeletal disease: Anyone taking calcium knows that you need to take it with vitamin D. It's needed because vitamin D promotes calcium absorption in the gut and maintains blood calcium levels to enable normal mineralization of bone and prevent abnormally low blood calcium levels that can then lead to tetany. Vitamin D insufficiency leads to secondary hyperparathyroidism (overly active parathyroid glands) that causes increased bone loss, osteopenia, osteomalacia, osteoporosis, and increased fracture risk.

Fall prevention is a public-health goal for the elderly. Each year, one in three people 65 years and older experiences at least one fall, with 5.6% resulting in a fracture, and vitamin D can play a role in preventing this. There are vitamin D receptors in human muscle that have a direct effect on muscle strength. A severe vitamin D deficiency can cause myopathy, which can cause muscle weakness and pain. Vitamin D supplementation can reverse this and improve balance. Supplementing 700-1,000 IU/day of vitamin D3 has been shown to possibly reduce falls by 19%-26%. Vitamin D3 at a dosage of greater than 800 IU/day given with calcium has been shown to reduce the risk of fractures by 10%-15%.

Another advantage to correcting a vitamin D deficiency has been seen in decreasing knee and hip pain. A longitudinal population-based cohort study of 769 randomly selected older adults aged 50-80 years found that moderate vitamin D deficiency predicts the incidence or worsening of knee pain over five years and possibly hip pain over 2.4 years.

Cancer: The link between the sun and cancer is typically not seen as a positive one because of the connection with skin cancer. UV-B radiation from the sun is said to be the most important environmental risk factor for nonmelanoma skin cancer. Because the sun is the primary source of vitamin D, researchers are looking to see what role it plays in skin cancer. Some believe that enough sun exposure to keep your vitamin D levels up while protecting your skin from damage is beneficial to skin cancer survival. There has also been research to show the protective effect that vitamin D has with the development of other cancers, including colon, breast, and prostate cancer.

In 1941, U.S. pathologist Frank Apperly published geographic data that demonstrated for the first time an inverse correlation between levels of UV radiation in North America and mortality rates from cancers. This means that more exposure to UV radiation (sun) leads to fewer deaths from cancers. Since this was published, it has been confirmed that there is an association between an increased risk of dying of various internal malignancies (for example, colon, breast, ovarian, melanoma, and prostate cancer) and living far from the equator. More research needs to be done to determine if there is a definite link between supplementing with vitamin D and the prevention of cancer.

View Slideshow Pictures
A female patient has her teeth examined by a dentist.

What does vitamin D do for your health? What are symptoms and signs of vitamin D deficiency? (Continued)

Cardiovascular disease: Vitamin D deficiency is associated with an increased prevalence of hypertension, hyperlipidemia, peripheral vascular disease, coronary artery disease, myocardial infarction, heart failure, and stroke. The anti-inflammatory effects of vitamin D may be the reason for this. Research is being done to determine exactly how this works and why.

Infections: Do you tend to get more respiratory infections in the winter? Vitamin D deficiency could be the cause. Observational studies have shown an association between low vitamin D status and an increased risk of both upper and lower respiratory tract infections. The role of vitamin D in reducing the risk of hospital-acquired infections, such as pneumonia, bacteremias, urinary tract infections, and surgical site infections is also being investigated.

Depression: The association between lack of sunlight and depressive disorders was first noted 2,000 years ago. Vitamin D plays a role in regulating adrenaline, noradrenaline, and dopamine production in the brain through vitamin D receptors in the adrenal cortex, as well as protecting against the depletion of serotonin and dopamine. This is the possible link with vitamin D's role in depression. The research is new in this area, and only the associations have been shown so far. Vitamin D deficiency has been associated with an 8%-14% increase in depression. Research is also finding a relationship with low vitamin D levels and increased risk of suicide. In a study done on the Department of Defense Serum Repository personnel, researchers compared the vitamin D levels of 495 verified suicide cases versus 495 controls. They found the lowest 25(OH)D level are associated with an increased risk for suicide. Another study compared vitamin D levels in 59 suicide attempters, 17 nonsuicidal depressed patients, and 14 healthy controls. The suicide attempters had significantly lower vitamin D than depressed nonsuicidal patients and healthy controls. Research is ongoing in this area to determine if you can prevent and treat depression by correcting vitamin D deficiencies.

An unhappy couple deals with erectile dysfunction (ED).

What does vitamin D do for your health? What are symptoms and signs of vitamin D deficiency? (Continued)

Multiple sclerosis: Evidence continues to accumulate supporting the role of vitamin D and the prevention and treatment of multiple sclerosis (MS). It begins with the vitamin D levels in pregnant women. Numerous studies have linked the occurrence of MS with birth month. There is a high prevalence of MS in high-latitude areas. The lack of sunlight exposure appears to be a significant predictor, and research is ongoing in this area.

Tuberculosis: Individuals with tuberculosis (TB) have been shown to have lower vitamin D levels than healthy people. Supplementation has shown to improve symptoms in these individuals. Further studies are needed to determine the cause and appropriate intervention.

Reducing the risk of type 2 diabetes: Research has shown that those with blood vitamin D levels over 25 ng/mL had a 43% reduced risk of developing type 2 diabetes compared with those with levels under 14 ng/mL.

Decreasing inflammation: Many of the health benefits associated with vitamin D may come from its role in decreasing inflammation. Research has shown a decrease in levels of C-reactive protein, a marker of inflammation, with increased levels of vitamin D to just below 21 ng/mL.

Reducing risk of allergies in children and adolescents: A nationwide study of over 6,000 individuals showed that allergic sensitization was more common in those with vitamin D levels under 15 ng/mL versus those with levels 30 ng/mL or more.

Sleep apnea: There is some evidence that vitamin D deficiency may increase the risk of obstructive sleep apnea brought on by inflammatory rhinitis and/or tonsillar hypertrophy. More research needs to be done to confirm this.

Decreasing dental cavities: A review of 24 controlled clinical trials encompassing 2,827 children found a 47% reduced risk of cavities with vitamin D supplementation.

Possibly helping with erectile dysfunction (ED): It is not clear if increasing your serum vitamin D levels can help with ED. Many men diagnosed with ED are diagnosed with cardiovascular disease (CVD) within a few years. Vitamin D deficiency is linked with CVD, so if you are deficient in vitamin D, some researchers believe that treating this could reduce your risk of ED.

A woman looks at the sun through a window.

What causes a vitamin D deficiency?

There are many possible causes of vitamin D deficiency.

Limited exposure to the sun

You may look out your window and see the sun shining and think that you are safe from this deficiency, but that is not always the case. Even in sunny climates there is an increased prevalence of vitamin D deficiency. We have all heard about the dangers of skin cancer and the need for sunscreen to protect us from this disease. This knowledge and the preventive actions we take have significantly decreased our vitamin D levels. Sunscreen protects so well against UV-B rays that an SPF of 30 decreases vitamin D synthesis in the skin by more than 95%. On top of this, we tend to spend more time indoors. One study found that it took Caucasians exposure of more than 30% of their body every day in the summer to make the optimal amounts of vitamin D. Most adults work indoors and wear more clothing during the work week, which leaves only about 10%-15% of their body exposed to UV for short periods, so they cannot meet their vitamin D needs through the sun alone. Even if you do have some exposure to the sun, the total amount of vitamin D you can produce is affected by the season, time of day, ozone amount, latitude, and number of clouds in the sky.

The important thing about using the sun for vitamin D production is to know that less is more. You are better off with short regular exposures to the sun rather than prolonged exposure for many reasons. The process is not as simple as the sun hitting your skin and vitamin D appearing in your blood. What actually happens is that vitamin D3 is first transformed by a process known as hydroxylation in the liver to 25-hydroxyvitamin D3, often written as (25(OH)D3), and then again in the kidney to its active form, 1,25-dihydroxyvitamin D3, written as (1,25(OH)2D3). The level that is checked in your blood is 25-hydroxyvitamin D, often written as 25(OH)D, which includes vitamin D2 and D3. By staying in the sun, you limit this process and can actually get less vitamin D. You also have a lower risk of burning and damaging your skin with short exposures.

The National Cancer Council in Australia recently published a position paper on ways to minimize the risk of skin cancer while maintaining adequate vitamin D levels via exposure from the sun. Currently, one-third of the population there is deficient. Extended and deliberate sun exposure without any form of protection when the UV index is 3 or above is not recommended for anyone. When the UV index is below 3, sun protection is not recommended, and it is recommended that people be outdoors in the middle of the day with some skin uncovered on most days of the week.

Darker skin

Melanin is what gives skin its color. Lighter skin has less melanin than darker skin. Melanin is able to absorb UV-B radiation from the sun and reduce the skin's capacity to produce vitamin D3 by 95%-99%. People with a naturally dark skin tone have natural sun protection and require at least three to five times longer exposures to make the same amount of vitamin D as a person with a white skin tone. African Americans have a population mean serum 25(OH)D level of 16 ng/mL, whereas white Americans have a level of 26 ng/mL.

A woman weighs herself on a scale.

What causes a vitamin D deficiency? (Continued)

Weight

Being overweight or obese may put you at risk for a vitamin D deficiency. A study done on 2,187 overweight and obese subjects found that those with a BMI above 40 had 18% lower serum vitamin D levels than those with a BMI under 40. Another study compared the vitamin D levels of 154 obese subjects to those of 148 nonobese subjects and found that the obese subjects' vitamin D levels were 23% lower. While diet and decreased sun exposure may have some impact on this, there appears to be an increased need that cannot be met without a supplement. One study tested the blood levels of vitamin D after sun exposure in both obese and nonobese subjects. Both saw an initial rise in vitamin D levels after similar exposures, but 24 hours later, there was 57% less vitamin D in the blood of the obese subjects. Both groups had a similar capacity of the skin to produce the vitamin. The difference was seen in the release of vitamin D from the skin into the circulation. It is believed that the fat under the skin holds onto the fat-soluble vitamin instead of releasing it, but more research needs to be done to confirm this. It is also not clear if weight loss causes an increase in vitamin D levels due to the fat cells releasing it into circulation. Some studies have shown small increases and others have not. Those who are losing weight should discuss the impact this may have on vitamin D levels with their health-care provider. For those who wonder if a vitamin D deficiency can contribute to weight gain, so far one study tested this and did not show this to be the case.

Who is at risk for vitamin D deficiency?

Research has begun to focus on who is deficient or insufficient in their vitamin D levels. Finding a deficiency does not mean that vitamin D is the cause of any ongoing symptoms. It simply means that there is a possible relationship, and more studies need to be done to clarify the relationship between vitamin D insufficiency or deficiency and disease processes.

Malabsorption

People with one of the fat malabsorption syndromes (for example, Crohn's disease or celiac disease) and people who have had bariatric surgery are often unable to absorb enough of the fat-soluble vitamin D.

Crohn's disease: A recent analysis of 63 studies on Crohn's disease (CD) found that there was a 57.7% prevalence of vitamin D deficiency in CD patients. They also found that the more severe the CD was, the lower the circulating vitamin D levels were.

Bariatric surgery: A review of 30 studies on patients undergoing Roux-en-Y gastric bypass and vertical sleeve gastrectomy found that preoperatively vitamin D deficiency was found in 13%-90% and insufficiency was found in up to 98%. The levels remained the same postoperatively. The research has shown a high level of insufficiency and deficiency levels in pre- and post- bariatric surgery patients, but no consensus has been established for the adequate dosage of vitamin D for prevention and treatment. The only way to know if the treatment is working is continued follow-up with your physician. The baseline vitamin D levels were lower in the African-American group, but all of the patients were able to achieve normal levels with comparable supplementation.

Age

Elderly: It has been shown that as we age our body has a decreased ability to synthesize vitamin D from exposure to the sun. There can be as much as 25% reduced production over the age of 70. While this can have an impact, it doesn't cause as much of a deficiency as the other risk factors.

Children: A study done in Ethiopia found that schoolchildren between the ages of 11-18 years were more likely to be overweight or obese when they were deficient in vitamin D. Another study of 301 students aged 11-19 years found that 12% of the students were deficient, and 53% had insufficiency. It also found that as body weight increased (measured by BMI) the level of vitamin D decreased.

Rheumatoid arthritis: A recent analysis of studies done on 1,143 patients with rheumatoid arthritis (RA) found that vitamin D levels were significantly lower in patients with RA compared to those without.

Fibromyalgia: The exact relationship between low vitamin D levels and fibromyalgia (FM) is unknown at this time, but there is an increased deficiency risk in people with FM. In a study of 150 patients with FM, 93% had deficient levels of vitamin D. In another study of 103 patients with FM or muscle pain, 75% had low vitamin D levels. Treating the deficiency resulted in 90% of them having improvements in their pain. The benefit on long-term bone health and muscle strength and the improvement in depression that can be found with treating vitamin D deficiency are all important for patients with FM and make it an important test for anyone with FM.

Medications and medical conditions

A wide variety of medications, including antifungal medications, anticonvulsants, glucocorticoids, and medications to treat AIDS/HIV, can enhance the breakdown of vitamin D and lead to low levels. There is also a loss of vitamin D for those with chronic kidney disease, primary hyperparathyroidism, chronic granuloma-forming disorders, and some lymphomas.

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A lab technician holds a blood test tube.

How is a vitamin D deficiency diagnosed?

All it takes is a simple blood test to find out if you are deficient in vitamin D, but you need to have the right test done. There are two blood tests for vitamin D. One is 1,25(OH)2D. This is one is not a good measure for your current vitamin D level. It has a short half-life and can be impacted by your parathyroid hormone (PTH), calcium, and phosphorus levels, so it's not a true measure of your vitamin D status. The preferred test is the 25-hydroxyvitamin D, written as 25(OH)D. This is the most accurate measure of your current status as it reflects what you get from your diet, from supplements, and from the sun. It is also the one that the majority of the research studies measures.Again, there are two sets of guidelines written by both the Institute of Medicine (IOM) and the task force for the Endocrine Society. These levels are for serum (blood) 25(OH)D:

  IOM Guidelines Endocrine Society Guidelines
Deficiency Below 12 ng/mL Below 20 ng/mL
Insufficiency 12 to 20 ng/mL 21-29 ng/mL
Adequate Over 20 ng/mL 30-60 ng/mL
Excessive Over 60 ng/mL  

In Europe, vitamin D experts have recommended a minimum of 20 ng/mL and state that more research needs to be done before raising it to 30 ng/mL. The question remains if the ideal level will be altered for people with different medical conditions. One study found that 25(OH)D levels and subsequent (50 years') risk of depression was lower in participants with levels between 20-34 ng/mL.

A man shops for vitamin D supplements.

What is the treatment for a vitamin D deficiency?

Vitamin D3 has been shown to be the best choice for supplements. Vitamin D2 supplements do not raise your levels the same amount as D3 and, in some cases, they have been shown to decrease levels over long-term use.

The amount of vitamin D that is needed to correct a deficiency will depend on the severity of the deficiency and your individual health risks. The time of year will also matter. For example, if you are on the low end of adequate blood levels and heading in to the winter months you would need a bit more than if you were heading in to the summer months. The goal for everyone is to get your stores to a safe level and prevent them from dropping with a maintenance plan.

What you take is as important as how you take it. Vitamin D supplements should be taken with a meal that contains fat. Studies have shown that when taken on an empty stomach versus with a meal containing fat, there was an average of 32% more vitamin D absorption in the fat-containing meal. This ranged from 11%-52%. Even an 11% reduction is significant and can impact your vitamin level. A recent study instructed people to take their supplement with their largest meal (typically the one with the most fat), and in three months, their blood levels went up an average of 56.7%.

There are supplements that can be taken on a daily, weekly, or monthly basis. It's a matter of preference and, most importantly, which one you will be more likely to take. You may start out at a higher dose and decrease after a month or two. Most experts feel that the goal is to get your level above 30-40 ng/mL, depending on your risk factors, and then take a maintenance amount. When you are deficient, it is recommended to have your blood tested after two to three months of taking the supplement to be sure that your levels are going up. Work with your doctors to find the optimal plan for you.

The task force for the Endocrine Society makes the following recommendations:

  • For children 1-18 years of age who are vitamin D deficient, we suggest treatment with 2,000 IU/d of vitamin D3 for at least six weeks or with 50,000 IU once a week for at least six weeks to achieve a blood level of 25(OH)D above 30 ng/ml, followed by maintenance therapy of 600-1,000 IU/day.
  • We suggest that all adults who are vitamin D deficient be treated with 50,000 IU of vitamin D3 once a week for eight weeks or its equivalent of 6,000 IU of vitamin D3 daily to achieve a blood level of 25(OH)D above 30 ng/ml, followed by maintenance therapy of 1,500-2,000 IU/day.
  • In obese patients, patients with malabsorption syndromes, and patients on medications affecting vitamin D metabolism, we suggest a higher dose (two to three times higher; at least 6,000-10,000 IU/day) of vitamin D to treat vitamin D deficiency to maintain a 25(OH)D level above 30 ng/ml, followed by maintenance therapy of 3,000-6,000IU/day. One study found that for every 33 lbs. of body weight the serum 25(OH)D level was 4 ng/ML lower at the end of one year of monitoring. This could lead to a significant change in the amount required to supplement based on your body weight and starting serum level.
  • African Americans: The population mean serum 25(OH)D level has been shown to be lower in African Americans than whites, but supplementation has been shown to be as effective in this population. A randomized, controlled vitamin D study was on a population of white and African-American women.

Quick GuideVitamin D Deficiency: How Much Vitamin D Is Enough?

Vitamin D Deficiency: How Much Vitamin D Is Enough?
Foods that contain vitamin D: Raw salmon filet, a glass of milk, fresh shiitake mushrooms, and canned tuna.

Is it possible to prevent vitamin D deficiency?

A few foods naturally contain vitamin D, and other foods are fortified with it. Most people can get at least some of their vitamin D needs from the sun. The amount found in food is not enough for treating a deficiency and may not be enough for most people to maintain adequate levels unless combined with sun exposure. Still, getting it from your diet when possible is a good idea.

  • 1 tsp cod liver oil has 400 to 1,000 IU/vitamin D
  • 3.5 oz salmon, fresh (wild) has 600 to 1,000 IU/vitamin D
  • 3.5 oz salmon, fresh (farmed) has 100 to 250 IU/vitamin D
  • 3.5 oz salmon, canned has 300 to 600 IU/vitamin D
  • 3.5 oz sardines, canned has about 300 IU/vitamin D
  • 3.5 oz mackerel, canned has about 250 IU/vitamin D
  • 3.5 oz tuna, canned has 236 IU/vitamin D
  • 3.5 oz shiitake mushrooms (fresh) has about 100 IU/vitamin D
  • 3.5 oz shiitake mushrooms (sun-dried) has about 1,600 IU/vitamin D
  • 1 egg yolk has about 20 IU/vitamin D
  • 8 oz fortified milk or yogurt has 100 IU/vitamin D
  • 8 oz fortified orange juice has about 100 IU/vitamin D
  • 3 oz fortified cheese has about 100 IU/vitamin D
View Slideshow Pictures
A chart displays the daily supplement intake tolerable upper limits for vitamin D.

What are symptoms and signs of an excessive vitamin D intake (Daily Limits Chart)?

In United States, the sales of vitamin D supplements went from $75 million in 2006 to $550 million in 2010; it is likely even higher today. This can be a case of too much of a good thing. Not many people realize that there is a limit to how much vitamin D you can safely take. This can build up in your fat cells and cause health problems. Tolerable upper limits (UL) are set to help avoid this.

Excessive intakes of vitamin D can lead to high levels of calcium (hypercalcemia). The symptoms of this are weakness, confusion, constipation, loss of appetite, and development of painful calcium deposits. Research has shown that very high doses can actually increase the risk of falls and fractures. A study of 2,256 community-dwelling women, aged 70 years or older, found that over five years, those given very high doses of vitamin D experienced 15% more falls and 26% more fractures then those in the placebo group.

To avoid this, keep your supplement intake below the UL:

  1 to 3 years 4 to 8 years 9 to 18 years19+ years
IOM 2,500 IU/day 3,000 IU/day 4,000 IU/day 4,000 IU/day
Endocrine Society 4,000 IU/day 4,000 IU/day 10,000 IU/day 10,000 IU/day

This limit is set as the most that a person can consume safely. The arguments against these levels stem from the fact that you can get 10,000-25,000 IU from exposure to the sun in one day. Studies have shown that supplementation over 10,000 IU/day can cause kidney and tissue damage. A recent study found that high-dose vitamin D supplementation (20,000-40,000 IU/week) caused a slight but significant increase in hemoglobin A1C and C-reactive protein, and a decrease in serum HDL. Currently, there are not enough credible studies to support the safety or necessity of taking a supplement in a dose that exceeds the current tolerable upper limits.

There is no disputing that fact that vitamin D plays many vital roles in our well-being. Changes to our lifestyle, diet, and supplementing when needed are the keys to curbing the vitamin D deficiency pandemic.

Reviewed on 6/9/2016
References
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