There
was an article (“Effects of vitamin D supplementation on
musculoskeletal health”) recently published on Lancet
Diabetes and Endocrinology;
it was a meta-analysis report reviewing 81 studies. The conclusion
is that normal individuals taking vitamin D supplements doesn't prevent
fracture or fall and may increase the risk of kidney stone.
I
gave a talk (to a Taiwanese community) on vitamin D some years ago,
in which I mentioned the statement of Institute of Medicine (IOM, now
called the National Academy of Medicine, is part of the National
Academy of Sciences, Engineering, and Medicine) in November 2011.
Vitamin
D is still important for bone health, I believe
The
following is from the Power Point of my talk. The IOM analyzed more
than 1,000 studies and interviewed the experts of various fields and
its conclusion “found evidences to be mixed and
inconclusive” using vitamin D on various conditions such as cancer,
hypertension, cardiovascular diseases, diabetes, metabolic syndrome,
immune responses, falls, neuro/psychological functions, physical
performance, pre-eclampsia and reproductive function.
 |
| Power Point of my talk |
But
IOM
says “current evidence supports vitamin D a role in bone health." IOM is known to be very conservative, having 10 or more members.
American doctors respect, but not necessarily follow its
recommendation, Just like Mark Twain says of classic, “a book which
people praise and don't read.”
Vitamin
D comes with many forms: Those come from foods are D2, skin (with
help of sun) D3; both are converted to 25(OH)Vitamin D in liver, then
to 1,25(OH)2 Vitamin D in kidney (this is the active form). Level of
25(OH)Vitamin D reflects vitamin D store, so when we check vitamin D
level, we measure blood 25(OH)Vitamin D level.
The
best source of vitamin D is your skin and sunlight (UVB)
It
is the ultraviolet B (UVB) in the sunlight that helps skin make
vitamin D, general speaking 10AM to 3PM is the better time to have
more UVB. In certain areas such as Boston, there is practically no
UVB reaches the earth in winter time (November to February). Skin
color also determines the efficiency, fair (white) skin has the best
efficiency, the dark skin (containing more melanin) the least
effective as the melanin competes for UVB with the vitamin D-making
cells. General speaking, it is enough to have 10% of body expose to
sunlight for 10 minutes a day for the fair skin.
Of
note, vitamin D2 (from food) is only 30% as effective as vitamin D3
(from sun) in maintaining 25(OH)Vitamin D level, that is why we sing
“you are my sunshine” with enthusiasm and admiration. Keep in
mind, the vitamin D store declines as we age. Ability of vitamin D
synthesis from skin also declines with age. We are led to believe
that vitamin D deficiency may lead to or accelerate osteoporosis
(骨質疏鬆症),
even though the Lancet
Diabetes and Endocrinology says
otherwise.
No
consensus for normal blood vitamin D level among professional
organizations
The
problem comes from the fact that there is no consensus opinion on the
normal vitamin D level among various professional organizations.
IOM
says the blood vitamin D level is 20 ng/mL or above, but National
Osteoporosis Foundation, International Osteoporosis Foundation and
American Geriatric Society all say 30-70 or even 30-100 ng/mL. Most
physicians go by the “30 to 70 or even 100” normal value.
The
best source of vitamin D is your skin and sun; few foods contain
vitamin D. Sea shells contain vitamin D, but not all sea foods do
(salmon, tuna and mackerel are exceptions) Cheese, egg and yogurt
have some vitamin D; this is why we have vitamin D fortified milk,
orange juice and cereals.
The
following table gives you some idea as to the
food sources of vitamin D:
Our
body cannot make vitamins, vitamin D is the only exception. Sometime
I wonder what is the God's purpose? It is either God knows few of our
foods contain vitamin D or vitamin D is more important than any other
vitamins.
There
is an ongoing vitamin D and Omega-3 trial (VITAL), a large study
(more than 25,000 participants) investigating whether vitamin D and
omega-3 supplements can lower the risk of cancer, heart disease or
stroke; the jury is not out yet.
If
one googles Internet, one will find innumerable articles that vitamin
D is good for almost all diseases of all organ systems, ranging from
cancer to Alzheimer disease, 而且有病治病,無病防身。對於這些報導我是姑且聽之.
But for bone health, I go by the normal vitamin D level of 30 ng/mL
or above (some say >50 may be detrimental). If one cannot
maintain the normal value with one's diet, then vitamin D supplement
is the way to go, especially during the winter time.
It
is of importance to maintain normal vitamin D level if one has
osteoporosis
In
case of having osteoporosis, in addition to the specific treatments
(bisphosphonates,
Prolia, Forteo, Tymlos, Evista, etc.)
One needs to strive to maintain normal vitamin D level and to ensure
adequate calcium intake.
 |
| Power Point of my talk |
An
article in 2014 British
Medical Journal says
“People with low vitamin D levels were more likely to die from
cancer, heart disease and to suffer from other illnesses.” However,
in 2014 the United States Preventive Services a Task Force (USPSTF—a
federal government agency) advised doctors not to do “routine” as
the benefits of taking vitamin D supplement in a healthy individuals
are not proven. 我買了一大瓶 vitamin
D 要給 Katy吃,我道她沒有每天認真吃,我也睜一眼
閉一眼。因為我也不確知她到底要不要吃。Some
experts warn that taking vitamin D supplement may increase risk of
kidney stone or calcification of the blood vessel wall. I believe
this may be a concern only for those taking excessive or mega doses of
vitamin D.
How
much vitamin D supplement one should have everyday?
Institute
of Medicine: for those age 1 to 70: 200-600 IU a day; age 71 or
above: 400-800 IU a day.
National
Osteoporosis Foundation: 800-1000 IU a day.
Endocrine
Society (of endocrinologists): 1500-2000 IU a day.