 INTRODUCTORY
LINKS
WHAT IS VITAMIN D?
Vitamin D is a hormone, not a vitamin. It is synthesized in the skin
and then converted to its active form by the liver and then kidney. (There
are exceptions to this which are not entirely worked out and are beyond
the scope of this website.)
SUNLIGHT PROVIDES ENERGY FOR CHANGE IN MOLECULAR STRUCTURE AND OPENS THE RING
STRUCTURE OF THE IMMEDIATE PRECURSOR TO CHOLESTEROL.
A single gel cap of Maximum D3® contains approximately the same
amount - of
the same human hormone - a light skinned person would make if exposed
to summer sun for a few hours.
Excellent introductions to the chemistry and actions of vitamin D and
other hormones can be found at:
Vitamin
D
(Thank you Colorado State )
http://vitamind.ucr.edu/about.html
(
UC Riverside)
WHAT DOES VITAMIN D DO?
Vitamin D's actions are best understood in its role in calcium metabolism.
Without it a person is not able to absorb the calcium in his or her diet
or maintain the proper balance of calcium and phosphorus to support bone
mineralization - build and maintain bones. Lack of vitamin D can also
cause over stimulation of the parathyroid gland and muscle weakness.
Recent studies have found that vitamin D receptors are present in most if not
all cells in the body. Experiments suggest that vitamin D has physiologic effects
much broader than just a role in mineral homeostasis and bone function. This
is an active area of research, but not well understood. This is an important
point because there has been interest in vitamin D and several cancers, menopause,
and effects on other organs. These are areas of research. (DeLuca Am J Clin
Nutr 2004; 80(suppl): 1689S-96S. Good current overview and starting
point for in depth study of vitamin D http://www.ajcn.org/cgi/content/full/80/6/1689S )
Persons promoting D vitamins for purposes other than bone and muscle really do
not have adequate data to make unproven claims.
WHAT IS THE CORRECT DOSE OF VITAMIN D?
Current literature suggests that the minimum amount of supplemental
D3 needed to maintain adequate blood levels in normal adults exceeds 1000
to 1400 IU a day. Maximum D3® was formulated to provide this threshold
when taken weekly. (Cholecalciferol can be taken daily, weekly, or even
less often -- with proportionally greater doses. Note that quality of
product becomes increasingly important with higher doses.) Dosage is
an issue which is still being investigated and which has a complex answer.
Sun exposure, diet and aging affect vitamin D production and metabolism.
Young adults (read young skin is better than old skin) do not as a rule
require supplementation if they are exposed to the sun on a regular basis.
This article is recommended as a starting point for a more in
depth explanation:
Estimation of optimal serum concentrations of 25-hydroxyvitamin
D for multiple health outcomes
Heike A Bischoff-Ferrari, Edward Giovannucci, Walter C Willett, Thomas Dietrich
and Bess Dawson-Hughes
http://www.ajcn.org/cgi/content/abstract/84/1/18 http://www.ajcn.org/cgi/content/full/84/1/18
And these articles are useful:
http://www.cmaj.ca/cgi/content/full/166/12/1541
Heaney A J of Clinical Nutrition 2004
http://www.ajcn.org/cgi/reprint/80/6/1706S
R. Vieth
Critique of the Considerations for Establishing the Tolerable Upper Intake Level for Vitamin D: Critical Need for Revision Upwards
J. Nutr., April 1, 2006; 136(4): 1117 - 1122.
http://jn.nutrition.org/cgi/content/abstract/136/4/1117
Safety studies have been done using 10,000 IU daily without observed
problems. This does not, however, mean that this dose would prove to
be harmless if long term studies were done on a large population. There
is no proven reason to take a great deal of cholecalciferol and there
are reasons to be cautious. For maintenance - not to treat deficiency
- 1300 daily or 10,000 IU weekly appear adequate and given present knowledge
it seems inadvisable to take more than twice these amounts. Remember
also that most persons would be expected to obtain some vitamin D from
other sources.
These recommendations apply only to D3 (cholecalciferol) and not to D2 which
is less potent and may have other issues.
ARE THERE NATURAL SOURCES FOR VITAMIN D?
Yes, but dietary sources are rarely adequate. The principal natural
source of vitamin D is sunlight. Exposure of the entire body to sunlight
to the point of mild redness will raise the blood level of vitamin D
about as much as 20,000 IU of D3. It has been estimated that full summer
sun exposure of the neck, back and arms for 15 minutes twice a week will
provide adequate vitamin D levels in young adults. Sun effect depends
on season and distance from the equator, age and pigmentation of the
skin.
Some fish oils are fair sources of vitamin D. A tablespoon of cod liver oil a
day should do the trick, but this amount presents the problem of too much vitamin
A.
MORE IS NOT BETTER!
As has already been stated, vitamin D is a hormone and has receptor
sites throughout the body. TOO MUCH MAY BE HARMFUL. The approximate desirable
blood levels and doses needed for bone health are known. MAXIMIM D3 was
designed to meet this need in normal persons and still provide a substantial
safety margin if other sources of vitamin D are consumed. |
