Vitamin D Supplement Uses, Benefits, Dosages, Side Effects & Interactions

Vitamin D is a fat-soluble vitamin that is often called the “sunshine vitamin”. Exposure to natural sunlight is one way to obtain this very important micronutrient.

Humans are able to produce vitamin D in their skin cells with exposure to ultraviolet B (UVB) rays. It can also be obtained in small amounts by eating certain foods. [1]

Vitamin D works inside the body to help maintain bone/teeth health and support the health of the immune system, brain, nervous system, lungs, and cardiovascular system.

This vitamin is also important for mood regulation and is required for the synthesis of several neurotransmitters. Levels of this vitamin in the body can influence obesity, skin health, joint function, risk of respiratory tract infection and more.

Vitamin D is part of a group of fat-soluble chemicals called secosteroids. They are known to increase intestinal absorption of zinc, calcium, phosphate, magnesium, and iron.

Research suggests that 10 minutes of sunlight exposure per day is adequate to prevent a deficiency in this vitamin. However, many people have low levels of Vitamin D and can benefit from using a supplement.

This article will discuss how vitamin D works in the body, different forms of this nutrient, common uses, health benefits, signs of deficiency, food sources, dosages and side effects.

Vitamin D

Vitamin Supplement

Mood

Bone Health

Immunity

How It Works:

• Essential for maintaining strong bones and teeth
• Supports immune function and well-being
• Supports mood balance and sleep patterns

Dosage:

Between 500 - 2000 IU per day

Safety:

Rated Likely Safe

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What is Vitamin D?

The term “vitamin D” is a misnomer because this nutrient is not a vitamin.

Vitamins are essential nutrients that cannot be synthesized in the human body. Vitamin D is not actually a vitamin, because it can be biosynthesized endogenously (within the body).

This compound is a prohormone. Prohormones are largely-inactive natural substances in the body that can be converted into active hormones.

There are five different forms of the fat-soluble Vitamin D: D1, D2, D3, D4, and D5.

The two forms that are physiologically important in humans are D2 (ergocalciferol) and D3 (cholecalciferol). Normally when a supplement lists “Vitamin D” as an ingredient, it is referring to either D2 or D3, or a combination of the two.

According to the Natural Medicines Comprehensive Database (NMCD), ergocalciferol is produced from yeast combined with a plant sterol called ergosterol. Cholecalciferol is produced inside skin cells from a cholesterol precursor called 7-dehydrocholesterol. [5]

Both D2 and D3 are biologically inactive until they undergo a process called hydroxylation. Via two separate enzymatic hydroxylation reactions, D2 and D3 are converted in the liver and kidneys into an active metabolite called calcitriol. [5]

Inside cells, calcitriol is used to promote the absorption of calcium and other important trace minerals in the intestines. [5]

In addition to its effects on calcium homeostasis, Vitamin D also is needed to facilitate the growth and repair of bones.

This vitamin increases bone matrix-secreting cells called osteoblasts and multinucleate cells called osteoclasts that are involved in bone resorption (gradual breakdown into component parts). [5]

Although its primary roles in the body relate to bone health, Vitamin D is also important for other functions. Some of these include neuromuscular function, growth of cells, and the inflammatory immune response. [5]

Th full scope of vitamin D’s mechanism of action in the body are not fully understood. Researchers continue to explore the effects of endogenous vitamin D and how it works as a dietary supplement.

Vitamin D Supplement Uses

The NMCD reports that people take supplemental vitamin D for many uses. Orally, it has been used for:

• Asthma
• Autoimmune diseases
• Cancer
• Cardiovascular health
• Chronic obstructive pulmonary disease (COPD)
• Cognitive function
• Enhancing immune function
• Influenza
• Multiple sclerosis
• Osteoporosis
• Plaque psoriasis
• Premenstrual syndrome (PMS)
• Respiratory tract infections
• Seasonal affective disorder (SAD)
• Tooth health [5]

There are dozens of other oral uses for vitamin D as well. Some of these include fibromyalgia, bronchitis, weight loss, Alzheimer’s disease, and vaginal atrophy.

Topically, creams containing this vitamin are used for plaque psoriasis, viral warts, and a noncancerous skin growth disorder called seborrheic keratosis.

Many of the uses described above require further clinical study to determine therapeutic efficacy. More research is needed to know whether supplementing with this vitamin works for these conditions or not.

These claims have not been evaluated by the US Food and Drug Administration. Dietary supplements containing Vitamin D are not sold or marketed for the prevention or treatment of any medical conditions.

The section below describes the research available on vitamin D and its effectiveness for various uses as seen in clinical research trials.

Vitamin D Health Benefits

Using a Vitamin D supplement may promote mood balance, bone health, immune function and general well-being.

This supplement is commonly taken to support sleep patterns, reduce anxiety and improve mood. It is also taken among elderly women who are particularly prone to osteoporosis.

According to PubMed, current research is focused largely on its effects in cancer, cardiovascular disease, obesity, pain management, depression, and diabetes. [3]

In 2016, researchers at the Tehran University of Medical Sciences reviewed the evidence available concerning this vitamin’s potential roles in multiple diseases.

They concluded that, “Adequate Vitamin D level can play a protective role in the incidence and development of breast cancer, hypertension, and osteoporosis”. [4]

The NMCD rates vitamin D as Effective for the following:

• Familial hypophosphatemia
• Fanconi syndrome
• Hypoparathyroidism
• Osteomalacia
• Renal osteodystrophy
• Rickets
• Vitamin D deficiency [5]

Vitamin D is rated as Likely Effective for:

• Corticosteroid-induced osteoporosis
• Osteoporosis
• Plaque psoriasis [5]

This means there is a preponderance of evidence suggesting efficacy, but more study is needed to confirm findings for all groups of people.

The NMCD rates vitamin D as Possibly Effective for:

• Dental caries/cavities
• Heart failure
• Hyperparathyroidism-related bone loss
• Multiple sclerosis
• Respiratory tract infections
• Tooth retention [5]

Preliminary evidence demonstrates benefits, but more study is needed to make a conclusive determination.

This nutrient is administered intravenously in premature infants to treat hypocalcemia tetany, a condition marked by involuntary muscle contractions caused by low calcium levels.

It is also used in injection form to treat low calcium and hyperparathyroidism in those undergoing renal dialysis. It is also used intravenously to treat osteitis fibrosa, a condition marked by tenderness and pain in bones.

Vitamin D is administered intramuscularly to treat a metabolic bone disease that sometimes occurs in patients with chronic liver disease called hepatic osteodystrophy [10].

It is also used for severe proximal myopathy (muscle disease) that is sometimes caused by vitamin D deficiency.

Medicinal vs. Supplemental Use

Endogenous vitamin D is involved in diverse physiological pathways within the human body. Researchers are interested in the effects of administering this vitamin in the form of a supplement.

Promising results have been seen in some clinical studies using vitamin D for Alzheimer’s disease, asthma, cancer, diabetes, hyperlipidemia (elevated blood lipids), polycystic ovary syndrome (PCOS), premenstrual syndrome, seasonal affective disorder (SAD), and weight loss.

This research is limited though, and more clinical trials are needed to determine the therapeutic efficacy for these uses.

High-dose vitamin D pills are regulated as prescription medications in the United States. Injectable forms of this vitamin are also used as a prescription therapy and are intended to be administered by a doctor.

Low-dose dietary supplements are available and are the most common form of this product used. These supplements typically contain 1000 IU of active ingredient per serving size.

However, these products are not approved by the FDA as drugs to prevent or treat any medical conditions. If you are interested in using Vitamin D to address a specific health concern, it is important to consult with a doctor to determine whether this product is appropriate for you.

Bone and Joint Health

Maintaining adequate levels of phosphorus and calcium in the body is imperative for long-term bone and joint health.

Vitamin D is required for intestinal absorption of these two important nutrients. This vitamin also helps to reclaim calcium that would otherwise be lost to renal excretion (urination). [5]

In children, being deficient in vitamin D can cause rickets. In this condition, impaired mineralization (hardening) causes soft leg bones and a resulting “bow-legged” appearance.

This is one reason why pregnant and nursing women are advised to intake higher amounts of this vitamin than other adult women. [12]

In adults, low levels of dietary intake can cause osteoporosis (brittle/fragile bones) or a condition where bones lose density and become soft called osteomalacia. [5]

Osteoporosis most often is caused by hormonal imbalances that result from chronic nutrient deficiencies, especially with regards to calcium and vitamin D. [2]

Osteomalacia often causes weakness in muscles and bones, commonly resulting in bone fractures of the humerus (upper arm), femur (upper leg), and/or spine. [2]

According to the Natural Medicines Comprehensive Database, most clinical research shows that, “taking cholecalciferol (vitamin D3) orally with calcium supplements can decrease postmenopausal bone loss, help prevent osteoporosis, and decrease the risk of fractures.” [5]

Based on the results from many clinical trials, the National Osteoporosis Foundation (NOF) recommends intake of 800-1000 IU of vitamin D per day for preventing osteoporosis in adults over 50 years old. [5]

According to one analysis, taking 700-800 IU of cholecalciferol per day either with or without calcium significantly reduces the risk of fractures in elderly people who are still ambulatory (able to walk) and living in care facilities. [5]

If you are interested in increasing your vitamin D intake for bone and joint health, it is recommended to discuss it with your doctor before starting.

Diabetes Mellitus

Some evidence suggests that vitamin D levels in the body may influence the development of diabetes.

Population research demonstrates that those deficient in vitamin D are significantly more likely to develop type 2 diabetes than those who are not deficient. Researchers are not sure if this reduced risk is independent of calcium intake. [5]

Some preliminary evidence associates daily vitamin D administration in first-year infants with reduced incidence of type 1 diabetes mellitus in later years.

In another analysis, researchers found a 29% reduction of risk for developing type 1 diabetes with routine vitamin D supplementation during early childhood. [5]

While multiple studies have suggested that vitamin D levels may alter the risk of developing diabetes, the results of clinical evidence using this supplement to treat type 2 diabetes is conflicting.

One analysis of available clinical trials showed that taking vitamin D can slightly reduce both insulin resistance and fasting blood glucose levels in those with impaired glucose tolerance (prediabetes) or type 2 diabetes mellitus. [5]

However, another meta-analysis of results reported no effects on fasting blood glucose levels in diabetic or prediabetic subjects. [5]

Researchers suggest that these conflicting results may relate to vitamin D status at baseline. In the second analysis it was found that a reduction in fasting blood glucose levels was seen in a subgroup of diabetic patients with vitamin D deficiency.

More clinical research is needed to determine the effects this vitamin may have on preventing or treating diabetes mellitus.

If you have been diagnosed with prediabetes or diabetes and are interested in vitamin D supplementation then speak with your doctor or endocrinologist.

Vitamin D and Cancer

Some population research has shown that there is an association with higher vitamin D levels in the blood and a reduced risk of cancer. [5]

There is a lot of scientific interest in studying the effects of supplementing with this vitamin on cancer. However, clinical evidence on the use of vitamin D for preventing cancer is conflicting.

Epidemiological studies have found a significantly reduced risk of breast cancer in premenopausal women who have a higher intake of vitamin D and calcium. Intake of this vitamin alone without increasing calcium is not associated with a decreased risk.

However, a large scale clinical trial from the Women’s Health Initiative found that 400 IU of vitamin D per day plus 1000 mg of calcium for 7 years did not cause a significant reduction in breast cancer risk in postmenopausal women. [5]

Research results on colorectal cancer are more promising. Multiple studies have shown that a high dietary intake of vitamin D or calcium supplements is associated with reduced risk of colorectal cancer and recurrence of adenomas (benign colon tumors that may develop into cancer). [5]

Vitamin D does appear to be an important factor in these situations, as people with below average levels of this vitamin do not appear to get any benefit from calcium supplementation alone.

A 2016 review of literature from the past two decades concluded that vitamin D, “presents oncoprotective actions through modulation of inflammation, cell proliferation, cell differentiation, angiogenesis, invasive and metastatic potential, apoptosis, miRNA expression regulation and modulation of the Hedgehog signalling pathway.” [7]

However, the reviewers state that much of the epidemiological evidence about vitamin D and cancer is still inconclusive.

They say that more reliable randomized controlled trials are warranted and necessary, “to discern the real effect of vitamin D in cancer risk reduction and therapy.” [7]

Vitamin D for Cardiovascular Health

According to a 2015 research review of studies on vitamin D for cardiovascular disease and diabetes, more research is needed to determine efficacy.

According to the reviewers, “It is possible to conclude that maintenance of serum Vitamin D levels holds advantageous aspects in diabetic and cardiovascular conditions… people should strive to attain them.” [8]

Research from Vanderbilt University Medical Center in 2016 reports that there is a growing recognition in the scientific community that vitamin D has various important actions in the body beyond promoting the health of the skeletal system and joints.

They note that low levels of vitamin D have been consistently associated with higher risk of cardiovascular disease. [9]

However, the available clinical research at this time has shown that compared to a placebo, taking cholecalciferol or ergocalciferol supplements either with or without calcium does not decrease the risk of heart attacks, stroke, or death in people with or without risk factors for cardiovascular disease. [5]

More research is needed to determine the therapeutic efficacy of vitamin D for cardiovascular diseases. If you are interested in taking supplements for cardiovascular health then speak with your doctor or cardiologist.

Vitamin D Deficiency

Dr. Edward Group III states that the causes of vitamin D deficiency are not clearly defined, but that poor diet, too little exposure to sunlight, and/or lacking exercise are typically involved in most cases.

Dr. Group says some risk factors for vitamin D deficiency are based on sex, ethnicity, and the amount of time spent being sedentary. [2]

Vitamin D Deficiency Syndrome (VDDS) risk is higher in those with various health disorders especially in cases of autoimmune disease, chronic fatigue, chronic pain, certain cancers, osteoporosis, and heart disease. [2]

Making sure you get enough of this vitamin is important, especially if you live in colder climates, are elderly and/or do not get outside regularly.

If you become deficient in vitamin D, you will be at increased risks for developing multiple adverse health conditions including MS (multiple sclerosis), cancer, and type 2 diabetes mellitus. [1, 2]

Having a low vitamin D status can worsen symptoms associated with rickets or bone/joint disease and swelling/pain in joints, muscles and/or fibrous tissues (rheumatism).

Deficiency can also cause calcium levels to drop, possibly resulting in a condition called hypocalcemic tetany. This can cause overexcitation of neuronal impulses, resulting in involuntary spasms of the larynx, hands and/or feet. It may also cause muscle cramping. [2]

Dr. Group says that symptoms of deficiency and related conditions improve by increasing consumption of vitamin D-rich foods, getting adequate sun exposure, or by routinely taking a supplement.

How to Increase Vitamin D Levels

The best way to increase levels of Vitamin D in the body is through safe, regular exposure to natural sunlight.

For fair-skinned people, approximately 10 minutes outside during the summer in midday sun can provide up to 10,000 units of cholecalciferol (D2). [13]

Dark-skinned individuals naturally produce lower levels of vitamin D from sun exposure and will need to spend longer in the sun. Very dark-skinned individuals may need as much as six times the sun exposure as fair-skinned people to make the same levels of this vitamin. [13]

Healthy exposure to UVB rays is the body’s most efficient method for increasing its vitamin D stores. Vitamin D is stored in fat cells reserved for use when periods of sunlight exposure are lacking. [12]

During the winter in northern climates, adequate vitamin D production from sun exposure is not possible because the UVB rays from the sun do not penetrate the atmosphere in significant amounts. [13]

Bodily stores may be sufficient if sun exposure was adequate during sunnier months, however eating foods high in vitamin D can help maintain levels and prevent a deficiency.

Dr. Josh Axe says there are some foods that contain vitamin D in appreciable amounts. Some of the best food sources include:

• Cod liver oil
• Eggs from chickens fed vitamin D-enriched feed
• Fatty fish including tuna, mackerel, sardines, salmon and herring
• Raw milk and other dairy products fortified with vitamin D [7]

You can also get more of this vitamin in your diet by eating mushrooms, beef liver, orange juice, soy milk, some cereals and caviar. There are various other foods with vitamin D in them not listed here.

Forms of Vitamin D Supplements

When possible, it is recommended to gain needed nutrients from organic food sources. However, this is not always possible, and in these cases, high quality supplements may be a helpful alternative.

Of the five forms of vitamin D known, the two that have been found to be usable in humans are D2 (ergocalciferol) and D3 (cholecalciferol). Dr. Mercola says that most doctors recommend D3 to their patients. [11]

In a meta-analysis involving more than 90,000 subjects, it was concluded that:

• Supplementing with D3 reduces overall mortality rates by 6%
• Supplementing with D2 increases mortality rates by 2% [11]

Vitamin D supplements are available in tablets, softgel capsules, gummies, and liquid drops.
Supplement dosages of this vitamin vary widely, with supplements ranging from 1000 IU per dosage up to 50,000 IU per dose.

The most common supplements provide between 1,000-10,000 IU and are intended to be taken daily. The very high-level dosages are intended to be taken every few days or weekly.

Vitamin D Dosage Guidelines

The Institute of Medicine published recommended daily allowance (RDA) values that approximate the intake necessary for the requirements of individuals in the general population. [5]

The RDA values for vitamin D for various age groups are:

• Infants up to 1 year old: 10 mcg (400 IU)
• Children 1-18 years: 15 mcg (600 IU)
• Adults 19-70 years: 15 mcg (600 IU)
• Adults over 70 years: 20 mcg (800 IU) [12]

The above daily recommendations were revised in 2010, but many health professionals believe them to be set too low.

They say this is because of emerging research that shows vitamin D to likely be much more significant to disease prevention and treatment than once believed. [12]

Dr. Mercola says that the recommendation for vitamin D3 that seems to be beneficial for most people is 200 mcg (8000 IU) daily. Most supplements provide between 1000-10,000 IU per dosage per day.

Dr. Mercola says that there is no optimal dosage that works for everyone. Instead, what matters is the amount of vitamin D found in the serum (blood).

According to Dr. Mercola, optimal levels of blood vitamin D are between 40 and 60 nanograms per milliliter of blood. [12]

If you have been diagnosed with a serious health condition like heart disease or cancer, he says the optimal level will be between 70 and 100 ng/ml. The only way to know your levels is to have blood work completed by your doctor.

Speak with your doctor to help determine the best vitamin D dosage for your needs.

Vitamin D Supplement Side Effects

The Natural Medicines Comprehensive Database has rated vitamin D supplements as Likely Safe when used orally or intramuscularly and appropriately.

This substance is rated as Possibly Unsafe when used orally in excessive dosages long-term. It is believed that taking dosages greater than the upper intake level (UL) of 4000 IU per day for long periods of time may cause hypercalcemia (elevated blood calcium levels). [5]

Dosages much higher than the UL (50,000 IU per week) may be needed for short-term periods to deal with complications linked to a deficiency. Usage of doses this high should be monitored by a doctor.

The NMCD states that vitamin D is generally well tolerated by most people when taken at appropriate amounts.

However, if you develop chronically high levels of this compound, toxicity can onset and possibly cause various adverse effects including bone pain, muscle pain, fatigue, headache, thirst, and/or lack of ability to focus.

More serious possible side effects associated with vitamin D toxicity include osteoporosis, pancreatitis, seizure, hypertension, and various dermatological disorders.

There are other possible side effects associated with inappropriate vitamin D intake not listed here. Speak with your doctor for more information about side effects of this vitamin.

Drug Interactions & Contraindications

Vitamin D may cause interactions with certain medications, herbal supplements, health conditions, and laboratory tests.

Some of the pharmaceuticals drugs it can interact with include:

• Atorvastatin (Lipitor)
• Calcipotriene (Dovonex)
• Cimetidine (Tagamet)
• Cytochrome P450 3A4 substrates
• Digoxin (Lanoxin)
• Diltiazem (Cardizem, Dilacor, Tiazac)
• Heparin
• Thiazide diuretics
• Verapamil (Calan, Covera, Isoptin, Verelan)

Vitamin D may also interact with blood thinners, diuretics, corticosteroids, stimulant laxatives, and sunscreens. It may interact with supplements that contain aluminum, calcium, and magnesium.

Vitamin D can affect certain health conditions including atherosclerosis, lymphoma, renal disease, hypercalcemia, and tuberculosis among others.

Seek professional medical advice before beginning to use vitamin D supplements for any purpose. Your doctor should know of any pre-existing conditions you have been diagnosed with that may cause interactions, as well as all medications and supplements you routinely use.

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