Vitamin D

What is Vitamin D?

Vitamin D is a group of fat soluble vitamins or prohormones. The two most common forms are D2 (ergocalciferol) and D3 (cholecalciferol). D2 can be obtained from plant sources while D3 is the form primarily synthesized in the skin by absorbing light energy from UVB rays. Vitamin D3 is considered to be the more bioavailable form of the vitamin and is the preferred form when supplementing.

Vitamin D obtained from sun exposure, food, and supplements. It is biologically inert and must undergo two hydroxylation reactions to be activated in the body. Calcitriol (1,25-Dihydroxycholecalciferol) is the active form of vitamin D found in the body.

The action for which vitamin D is best known is regulation of calcium and phosphorus concentrations in the blood. Vitamin D enhances the absorption of these two minerals in the small intestine; if dietary intake of calcium falls below adequate levels, vitamin D, in conjunction with parathyroid hormone, will mobilize calcium stores from the bones into the blood. Vitamin D is also necessary for bone growth and remodeling.

Approximately 5,000 research papers have been written about vitamin D in the last 40 years. Only recently have we begun to appreciate vitamin D's influence on many aspects of health beyond building healthy bones.

Vitamin D Deficiency

Vitamin D Deficiency has Been Linked to:

Various forms of cancer including breast, prostate and colon cancer
Fractures
Hypertension (High Blood Pressure)
Heart Disease
Pain and Muscle Aches
High CRP Levels
Insulin Resistance
Decreased immunity and lowered resistance to influenza and viruses
Osteoporosis and osteomalacia
Depression
Seasonal Affective Disorder (SAD)
Periodontal Disease
Tuberculosis
Chronic Pain
Peripheral Artery Disease
Cognitive Impairment
Type I Diabetes
Parkinsons
Autoimmune Disorders
Multiple Sclerosis

As vitamin D is becoming increasingly recognized as important to health, more doctors are doing blood tests for vitamin D levels to assess the nutritional status of this vital substance.

Vitamin D from Food

Vitamin D occurs freely in relatively few foods. Fish contain vitamin D because they are directly or indirectly nourished by algae which create the vitamin D from exposure to ultraviolet sunlight in shallow waters. Natural sources of vitamin D include:

Fish liver oils (cod liver oil provides 1350 IU per Tbs.)
Herring (1383 IU in 3 oz.)
Catfish (425 IU in 3 oz.)
Salmon (360 IU in 3.5 oz.)
Mackerel (345 IU in 3.5 oz.)
Sardines (250 IU in 1.75 oz.)
Tuna (200 IU in 3 oz.)
Eel (200 IU in 3.5 oz.)
One Egg (20 IU each)
Beef Liver (15 IU in 3.5 oz.)

The practical reality is that, on average, the U.S. diet provides 100 IU/day. That includes the contributions from vitamin D fortification of foods.

Vitamin D from Sunshine

The human body is incredibly efficient at creating vitamin D from sun exposure. It is estimated that full-body exposure for a few hours will create 10,000 IU of vitamin D. The full exposure necessary for vitamin D production is present in the tropics year around, at mid latitudes in the summer months only and not at all in the upper latitudes and arctic areas. Add to this the reduced exposure from spending most of ones time indoors, covering the skin with clothing and using sunscreen when in the sun. The result is that very few individuals are getting adequate vitamin D from their exposure to the sun. Concerns over skin cancer from excess sun exposure have caused some doctors to recommend limiting sun exposure and using sunscreen and protective clothing. More recently, some doctors have concluded that obtaining the vitamin D is more important than avoiding sun exposure to reduce skin cancer risk.

How Much Vitamin D do We Need?

Adequate Intake has been defined as 200 IU/day for ages infant to age 50, 400/day for ages 51-70, and 600/day for ages over 70. Note that these numbers are derived from early research that showed that this was the intake required to prevent the manifestation of gross deficiency symptoms like rickets and osteomalacia.

The American Academy of Pediatrics argues that these recommendations are insufficient and instead recommends a minimum of 400 IU, even for infants. The 100% Daily Value used for product labels is 400 IU. The National Institute of Health has set the safe upper limit at 2000 IU, but acknowledges newer data supporting a UL as high as 10,000 IU/day.

More recent research is indicating that these numbers are very inadequate for optimum health. In one study, the researchers noted that only children receiving the equivalent of 2,000 IU a day of vitamin D had the necessary increases in vitamin D levels to the 30 nanograms per milliliter level considered optimal for adults. There was no evidence of vitamin D intoxication at the 2,000 IU a day dosage. The researchers noted that there is a high prevalence of low vitamin D levels across all age groups worldwide and that many adult diseases are rooted the pediatric age group.

Vitamin D Toxicity

Because synthesis of the most active form of vitamin D is tightly regulated by the body, vitamin D toxicity usually occurs only if excessive doses are taken. Vitamin D 1000 ?g (40,000 IU)/day produces toxicity within 1 to 4 mo in infants. In adults, taking 1250 ?g (50,000 IU)/day for several months can produce toxicity. Vitamin D toxicity can occur iatrogenically (caused by medical treatment) when hypoparathyroidism is treated too aggressively. Of all published cases of vitamin D toxicity for which a vitamin D amount is known, only one occurred at a level of intake under 40,000 IU per day.

Vitamin D toxicity symptoms may include anorexia, nausea, and vomiting often followed by polyuria (excess urination), polydipsia (excess drinking), weakness, nervousness, pruritus (itching), and eventually renal failure. Proteinuria, urinary casts, azotemia, and metastatic calcifications (particularly in the kidneys) can develop. Most of the symptoms and effects of excess vitamin D are related to the increased calcium levels that result.

Vitamin D is contraindicated in individuals with elevated blood calcium levels or hypercalcemia. Individuals with kidney disease and people who use digoxin or other cardiac glycoside drugs should consult a physician before using supplemental vitamin D.

Vitamin D Drug Interactions

Some medicines interact with vitamin D.

The following medications may increase the need for vitamin D.

Anticonvulsants
Bile Acid Sequestrants
Cimetadine
Colestipol
Estrogens
Flurbiprofen
Gabapentin
Heparin
Hydroxychloroquine
Indapamide
isoniazid
Mineral Oil
Neomycin
Oral Corticosteroids
Orlistat
Phenobarbital
Sodium Fluoride
Valporic Acid

The following medications may have complex interactions with vitamin D and a physician should be consulted when combining vitamin D with these medications.

Verapamil
Warfarin
Allopurinol
Estradiol
Estrogens
Medroxyprogesterone
Thiazide Diuretics

These lists are not comprehensive. Exercise due diligence and always ask your pharmacist about potential interactions.

Vitamin D Supplements

Here are some recommended Vitamin D Supplements.

Vitamin D3 5000 IU

Vitamin D3 with Sea-Iodine 5000 IU

Vitamin D3 1,000 IU

Vitamins D and K with Sea-Iodine

Vitamin D References

Click to Expand References

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