Vitamin D3 is one form of D vitamin produced by the
cholesterol in the skin, when the skin comes in direct action with the
sunlight. Vitamin D3 is essentially inactive until biotransformed into
25-hydroxy-vitamin D3 in the liver, becoming five times more active than
D3, and then into 1,25-dihydroxy-vitamin D3 in the kidneys, becoming ten
times more active than D3.(1)
The combined actions of the vitamin
D3 network facilitate three key domains influencing the achievement and
maintenance of optimal bone mineral density throughout life. Firstly, they
are critical to the absorption of calcium from the intestines, and
depletion of vitamin D3 for whatever reasons results in severely limited
calcium absorption. Secondly, vitamin D is necessary for recouping
excreted calcium found in the kidney glomerular filtrate. Such facilitated
recouping helps to avoid continuous exaggerated urinary calcium loss. And
thirdly, 1,25-dihydroxy-vitamin D3 is instrumental in incorporating
calcium in the bone, boosting bone mineral density.(1)
A less
well understood action of vitamin D is its facilitation of cellular
differentiation. Proper cell differentiation lowers the risk of cancer. It
is of interest that the incidence of breast cancer is observed to rise in
proportion to the distance from the equator and this has been interpreted
to mean reduced endogenous vitamin D3 is involved in breast cancer risk,
and probably other cancers as well. Those with a history of cancer in
themselves or in their families may be well advised to ensure higher
levels of vitamin D3. There is a resurgence of interest in vitamin D for
its health enhancements beyond bone health. The biotransformation of
vitamin D3 into its more active metabolites depends on enzymes that use
magnesium as a cofactor. North American magnesium depletion is
accumulative and widespread because of food processing, refinement, and
soil exposures to commercial fertilizers.(4) Thus, magnesium depletion is
very likely a factor in age-related bone-thinning through a decline in the
maximally active 1,25-dihydroxy-vitamin D3. Thus, along with the obvious
need for calcium and vitamin D3, magnesium supplementation should be
recommended in those who are trying to arrest or reverse osteoporosis. The
typical recommendation is 2 parts of calcium to 1 part of magnesium.
Adding magnesium to the equation is calculated to overcome magnesium
depletion that can be exacerbated when only calcium is supplemented
because calcium competes with magnesium for the same intestinal absorption
site. As well, magnesium will enhance formation of greater calcium crystal
strength by optimizing calcium crystal size and shape.(4,5)
Dietary and supplemental vitamin D3 is oil soluble and can only be
absorbed via oil absorption, making it necessary for D3 supplementation to
occur with fat/oil containing meals. Age-related decline in fat/oil
absorption is a factor in diminished D3 absorption, and clinically
determined D3 deficits may be required to adequately compensate in the
treatment of osteoporosis.
Many consumers and physicians fail to
emphasize vitamin D3 supplementation in bone health enhancement. This
probably stems from assuming that sufficient vitamin D3 can be produced in
the skin. In children and younger adults, exposure to sunlight in the
spring, summer, and fall is expected to be adequate for producing enough
vitamin D3 for those seasons, particularly since it is also acquired in
milk and egg yolks. Perhaps special attention to supplementation of
vitamin D3 in this younger set during the winter season would be well
advised. However, optimal vitamin D3 levels in older Canadian adults may
become effectively diminished over time. Firstly, there may be
life-related reductions in exposure to the sun in general and there is a
natural reduction of solar energy reaching northern latitudes in the
winter months. Furthermore, in the winter there is less time spent outside
and more of the body is covered. But secondly, despite solar exposure
issues, there is a natural age related decline in our ability to produce
adequate amounts of vitamin D3 in the skin, and its subsequent activated
derivatives in the liver and kidneys. These factors make vitamin D3
supplementation an important consideration.
How much is
recommended? The Recommended Dietary Allowance (RDA) of vitamin D3 stated
above may not supply the optimal amount for adults. The RDA values
typically only address nutritional needs for avoiding deficiency
disorders, not the nutritional needs for optimal bodily performance. Many
proactive women supplement with calcium and vitamin D3, using 400 to 800
IUs. This practice has not been found to be problematic in Canada, even
when commenced in teenage years. In fact, the best defense against
osteoporosis in the senior years is thought to be the attainment of
maximal bone mineral density in the early life years before 20-25. Both
male and female teenagers and young adults should focus on early maximal
bone mineral density. Those with diagnosed thinned bones or full-blown
osteoporosis can safely increase their calcium handling efficiencies with
800 to 1000 IUs per day. Even a subtle protracted deficiency of vitamin D3
leads to increased risk of bone loss over time and osteoporosis
fractures.(6)
Numerous studies document that up to 80% of all hip
fracture patients may exhibit vitamin D deficiency.(7) There is a growing
clinical recognition of vitamin D deficiency in the general population,
leading to the conclusion that current levels of so-called adequate intake
are too low.(2,6,8) Separate clinical investigations using 700 and 800 IUs
instead of the usual 400 IUs have demonstrated lower hip fracture rates
compared to placebo.(2) The omission of vitamin D3 supplementation by
those with thinned bones or full-blown osteoporosis is a strategic error
in judgment by physician and patient. The margin of safety is substantial
for vitamin D, with toxicity being associated with a daily amount greater
than 2400 IUs, allowing an easy comfort level with 800 to 1000 IUs per day
for adult bodies.(2)
Men also develop osteoporosis, and our
Canadian insight can be taken from the American experience. The National
Osteoporosis Foundation reports that in the United States each year, men
suffer 33% of all the hip fractures that occur, and 33% of these men will
not survive more than a year. In addition to hip fracture, it is known
that men experience some painful and debilitating fractures of the spine,
wrist, and other bones due to osteoporosis.(9)
Vitamin D3 is oil soluble and can be absorbed only via
fat/oil absorption, making mealtime dosing the best time to supplement.
The higher the dose of vitamin D3, the greater is the need of fat or oil
in the meal. Vitamin D absorption can also be enhanced if nutritional oils
like flaxseed oil, Evening Primrose oil, or fish oils are taken with
supplemented vitamin D. Those with chronic fat absorption problems should
be investigated for vitamin D and bone status.
Use of Olestra has
been reported to diminish absorption of the fat-soluble vitamins, A, D, E,
and K. Magnesium supplementation is required to convert vitamin D2 to D3.
Many food and milk producers use vitamin D2 as their added vitamin D
component. Magnesium is also required as an enzyme cofactor for converting
D3 to 25-hydroxy-D3 and 1,25-dihydroxy-D3, the most active forms of
vitamin D3.
Bile acid sequestrants like Cholestyramine,
corticosteroids, Dilantin, barbiturates, Phenobarbital, etidronate,
tuberculosis drugs, and mineral oil interfere with vitamin D absorption
and/or metabolism.(1,3)
1. Murray, Michael T., Encyclopedia of Nutritional
Supplementation, Prima Publishing, Rocklin, CA, 1996 2. Utiger, Robert
D., editorial, The Need For More Vitamin D, New England Journal Of
Medicine, 338:12, 828-829, 1998 3. Graedon, Joe, Teresa Graedon, Deadly
Drug Interactions, St Martin Griffin, New York, 1995 4. Gaby, Alan R.,
Preventing and Reversing Osteoporosis, Prima Publishing, Rocklin, CA,
1994 5. Cohen, L., Kitzes, R., "Infrared spectroscopy and magnesium
content of bone mineral in osteoporotic women", Israel Journal of Medical
Science, 17: 1123-1125, 1981 6. Compston, J.E., Vitamin D Deficiency:
time for action, editorial, British Medical Journnal, 317: (Nov 28),
1466-1467, 1998 7. Brown, Susan E., Better Bones, Better Body, Keats
Publishing, New Canaan, CT, 1996 8. Thomas, Melissa K., Hypovitaminosis
D In Medical Inpatients, New England Journal Of Medicine, 338:12,
777-783,1998 9. The National Osteoporosis Foundation,
www.nof.org
These statements have not been evaluated by the Food and Drug Administration (FDA). Products are intended to support general well being and are not intended to treat, diagnose, mitigate, prevent, or cure any condition or disease. If conditions persist, please seek advice from your medical doctor.
