Vitamin D

View the Vitamin D presentation.

Contents

 

Sources of vitamin D

a.) Vitamin D metabolism

Vitamin D is a fat soluble steroid hormone produced in the skin when it is exposed to ultraviolet light of the UVB spectrum ( 290 - 315 nm). It commonly is known as the "sunshine vitamin" as a result. Melanin, sunscreen, season, latitude, time of day, weather conditions, clothing and a persons age all influence how much vitamin D can be made.

Essentially 7-dehydrocholesterol in the skin is converted to previtamin D3 by the UVB which is then further converted by a thermal conversion to vitamin D3 in the skin. Further processing occurs firstly in the liver to 25 hydroxy D3, which is the major circulating form and is the form commonly measured in the blood tests for vitamin D and then in the kidney to 1,25 di hydroxy D3, which is the biologically active form, also known as calcitriol. Only a small amount of the 1,25 di hydroxy vitamin D3 circulates in its free form to bind to the Vitamin D receptor ( VDR ) which is present in many tissues and cells throughout the body.

A recent consensus statement by the Australian and New Zealand Bone and Mineral Society, The Australasian College of Dermatologists, The Cancer Council and Osteoporosis Australia states that "during summer the majority of people can maintain adequate levels from a few minutes of exposure to sunlight on their face, arms and hands or equivalent area of skin on either side of the peak UV periods ( 10 am - 3 pm ) on most days of the week. In winter in the southern parts of Australia where the UV radiation levels are less intense, people may need about 2 - 3 hours of sunlight to the face, arms and hands, or equivalent area of skin, spread over a week to maintain adequate vitamin D levels."

b.) Other sources of vitamin D

Vitamin D can also be obtained from the diet as D3 in oily fish such as salmon, mackerel, sardines and herring, as well as from dairy foods and some fortified foods such as margarine but in general the major source of vitamin D3 is from sunlight. Vitamin D2 can also be obtained from some plant sources such as sun dried mushrooms and supplements and is then converted to vitamin D3 after ingestion.

Vitamin D3 can also be obtained from eating cod liver oil however this also contains a large amount of vitamin A, or by vitamin D3 supplements of which there are several on the market. Some of the supplements contain vitamin D3 and calcium but single vitamin D3 is also available.

 

Vitamin D benefits

A list of important vitamin D effects

 

Lack of Vitamin D

Causes of vitamin D deficiency include:

 

Consequences of Vitamin D deficency

 

Vitamin D blood test

While there is no consensus as to the most protective level of vitamin D against the many chronic diseases listed, the Australian and New Zealand Bone and Mineral Society, Osteoporosis Australia, The Australasian College of Dermatologists and the Cancer Council Australia recommend that for healthier bones the level of vitamin D – 25 hydroxy vitamin D - should be over 75 nmol/l.

That is the first benchmark I recommend to my patients.

Therefore in my patients whenever I check for a vitamin D level, a reading under 75nmol/l is defined as insufficient.

Observational studies have estimated that 50%reduction in bowel cancer incidence can be achieved if vitamin D is maintained over 87 nmol/l and 50% reduction in breast cancer incidence if vitamin D can be maintained over 137 nmol/l. To achieve these levels supplemental vitamin D is frequently required or improvement with diet.

 

Treatment of vitamin D insufficiency

 

Toxicity of vitamin D

Toxicity is reported to include nausea, thirst, headache, constipation, kidney stones, high calcium, vomiting, disorientation and coma if levels over 375 nmol/l are reached. Some studies report even higher levels are needed for toxicity.

In none of the patients taking supplements under monitoring at my practice has there been any toxicity seen and no levels over 300 have been documented.

 

References