VITAMIN D AND BONE HEALTH; WHAT IS ENOUGH?
As most people know, adequate calcium intake is
critical for maintaining bone health and preventing osteoporosis. Most
people also know that adequate amounts of vitamin D is also critical for
assuring the calcium will be absorbed. But what is enough vitamin D? The
research coming out the last few years is finally answering that
question.
The issue of how much vitamin D to take is only an
issue because we don’t live the way we evolved. Remember, unlike all
other vitamins, vitamin D can be created in our own bodies. It is
created in our skin from a cholesterol precursor by contact with
ultraviolet radiation (UVB) from good old sunlight. Our human ancestors,
if we go back many many years, spent most of their lives outside in the
sun and mainly in low latitudes such as the tropics. Without clothing to
get in the way this kind of sun exposure created plenty of vitamin D,
far more than the average American gets. Now we spend most of our time
indoors, when in the sun our skin is protected by clothing or sunscreen,
and many of us live above the 35-degree latitude where the angle of the
sun limits the exposure of ultraviolet light.
There are several factors that influence calcium
absorption but the first step is to ingest enough. The current
recommendation for osteoporosis prevention is that a woman over 50
should get 1200 mg of calcium per day from food and supplements (1000 mg
for women 50 and under and the same for men). However, calcium alone
does not maximize the potential for maintaining bone health. Other
factors include magnesium, manganese, zinc,
copper, boron, strontium, silicon, vitamin K, folic acid, vitamin B12,
vitamin C and, of course, vitamin D.
People absorb in the range of 15 to 45% of the
calcium ingested. Recent research shows that
low amounts of vitamin D means that your absorption is going to be
around the 15% range and adequate amounts of vitamin D will put your
absorption around the 45% range. That is three-fold difference in the
amount of calcium your body absorbs from the ingested calcium in the
food and supplements. That is likely to be the difference between
getting osteoporosis and not.
So what is enough vitamin
D? The historical recommendation of 200 I.U.s of vitamin D per
day (400 for women 50 and older) came from clinical experience that this
amount was enough to prevent rickets. Until fairly recently there was no
way of directly measuring the level of vitamin D in the body.
Consequently, there was no way to thoroughly study what intake levels
were adequate to prevent disease. Now that blood
(serum) levels can actually be measured we have seen an explosion
of published research in the last few years.
Previous “normal”
ranges of serum
25-hydroxycholecalciferol (commonly called 25(HO)D - the measure of
vitamin D in the serum) of less than 20 ng/mL were considered
to be a deficiency. However, the latest
research shows that a minimum of 32 ng/mL is necessary for
adequate calcium absorption. That is quite a difference.
By the end of the summer outdoor workers in
temperate latitudes like ours have serum levels of 60 ng/mL. People who
live in the topics and spend a lot of time outdoors have levels higher
than this all year-round. Clearly the old standard for “normal”
levels of serum vitamin D are too low!
Vitamin D lasts about 60 days in the body so even
people who have gotten plenty of sun in the summer will start becoming
deficient by late fall in latitudes above 35 degrees, such as the
Midwest. We could all move to the topics but supplementation is probably
more practical.
Vitamin D is an oil soluble vitamin so too much can
be toxic. The Institute of Medicine says that 2000 I.U.s of vitamin D
per day is the upper limit of safety. However, this is another one of
those old numbers that is no longer consistent with the research.
Research shows that during the winter months it takes 5000 I.D.s per day
from food or supplementation to get to the 60 ng/mL that is normally
found in the serum of those outdoor summer workers. Another study found
that it took 40,000 I.U.s per day to get up to serum levels associated
with toxicity.
It is clear to me, and many other people, that the
maximum safe dosage of vitamin D is much much higher than 2000 I.U.s per
day currently recommended by the Institute of Medicine. Even some
dietitians who work in calcium research are now saying that 3500 to 5500
I.U.s a day from all sources is required to maintain adequate serum
levels of vitamin D.
What about getting your vitamin D from sun
exposure? It is often recommended that if you get direct sun exposure
throughout the year you can maintain adequate levels of vitamin D. The
recommendation varies depending on the source - I’ve seen
recommendations vary from 20 minutes of exposure to face and arms twice
a week to10 to 15 minutes daily to 40% of your skin surface. Non-sunburning
sun exposure is clearly a good idea - it is the natural way to get your
vitamin D. However, this will probably be inadequate to maintain vitamin
D reserves unless you live in the tropics year-round. And it is simply
impossible if you live in Nebraska or any other area that is above 35
degrees latitude (Omaha is 41 degrees north). In addition, dark-skinned
people need even more sun exposure to get the same amount of vitamin D
production. So if you live here, sun exposure alone isn’t going to do
it.
Current research shows that during the autumn,
winter and spring an intake of vitamin D in the standard recommended
doses of 200 to 400 I.U.s per day will not produce the minimum
level of serum 25(HO)D necessary for healthy bones. That means that
almost no one in this region of the country (man, woman or child) has
adequate serum levels of vitamin D. What a surprise that as so many
women reach middle age they are being diagnosed with osteopenia and
osteoporosis.
For osteopenia and osteoporosis patients I am now
recommending 2000 to 4000 I.U.s per day of vitamin D when there is
little summer sun exposure (along with calcium and the other healthy
bone cofactors). If you don’t spend much time outdoors in the summer
without sun protection, supplementation would need to be year-round. It
is also advisable for these patients to get their serum 25(HO)D level
check periodically to make sure it is staying above 32 ng/mL. For many
reasons (see below) every adult, men and women alike, should be getting
more vitamin D than is common today. Finally, supplementation must be
with D3 (cholecalciferol - the natural human form) and not D2 (ergocalciferol
- as found in “vitamin D” enriched milk).
VITAMIN D: GOOD FOR MUCH MORE THAN BONES!
The benefits of adequate amounts of vitamin have
been all over the news. New studies are being published almost everyday.
Here is a summary of some of it:
* Overall reduction in mortality. One meta-analysis
(a study of many studies) showed a 7% lower risk of death overall during
the six-year period studied.
* Improved immune function. One study showed a drop
in colds and flu by 70% over three years with supplemental vitamin D.
The natural loss of vitamin D reserves in the autumn corresponds
directly to the onset of the cold and flu season. Is this the reason
there are so many more infections in the fall and winter?
* Reduction in heart disease. Those who supplemented with vitamin D had a 31% lower risk of
dying of heart disease in one study. Another found patients with chronic
heart failure had lower levels of vitamin D than others. Vitamin D has
also been associated with reducing blood pressure.
* Less cancer risk. Both breast and colon cancer
has been shown to be less likely with adequate amounts of vitamin D. A
study on colon cancer showed that those with higher serum levels of
vitamin D had a 72% less chance of dying from colorectal cancer than
those people with the lowest levels.
* Reduced diabetes and insulin resistance. Babies
supplemented with vitamin D in Finland the first year of life had over
80% reduction in the risk of getting type I diabetes. Another study
showed that adequate serum levels of vitamin D compared to those without
showed 60% less insulin resistance, which leads to less metabolic
syndrome and less type II diabetes. Plus normal insulin secretion is
dependent on vitamin D.
* Lower risk for MS. A study showed a 40% lower
risk for MS in those who supplemented vitamin D. Another suggested that
those who spend more time in the sun had lower risk than those that
stayed out of it.
* May help prevent inflammatory diseases like
rheumatoid arthritis and inflammatory bowel disease (Crohn’s disease,
ulcerative colitis, etc.).
VITAMIN D IN SUMMARY:
* No one living in the higher latitudes should
supplement with less than 1000 I.U.s of vitamin D per day unless it is
the summer and they are out in the sun without protection regularly. For
many people, if not most, it should be higher amounts. Researchers are
currently calling for changing the recommended doses to a range of 1000
to 2000 I.U.s per day (to be adjusted for summer sun exposure).
*
Women (or men) with osteopenia and osteoporosis
should be taking at least 2000 to 4000 I.U.s of vitamin D per day (along
with calcium and the other healthy bone cofactors).
* When possible get your serum 25(HO)D level
checked periodically to make sure it is staying above 32 ng/mL.
* Only supplement with D3 (cholecalciferol); never
D2 (ergocalciferol).