A fast-growing
body of evidence indicates that vitamin D likely ranks among the
most powerful anti-cancer agents in the human body.
Most of the evidence comes from epidemiological research, in which
scientists look for significant links between foods or individual
nutrients and health among large groups of people.
Just last week, we reported the results of an epidemiological study
from Harvard Medical School, showing that pre-menopausal women who
consume higher amounts of calcium and vitamin D may lower their risk
of developing breast cancer by almost 40 percent. (See “Vitamin
D + Calcium May Cut Pre-Menopause Breast Risks”.)
And the results of a new study from Nebraska add more evidence, this
time from a relatively small but rigorously controlled clinical
trial.
In brief, its authors found that women who took calcium and
vitamin D supplements had 60 to 77 percent fewer cancers,
compared with women who took placebo pills, and vitamin D was
credited as the key factor.
As the authors said, “Our findings of decreased all-cancer risk with
improved vitamin D status are consistent with a large and still
growing body of epidemiologic and observational data showing that
cancer risk, cancer mortality, or both are inversely associated with
[vitamin D-generating] solar exposure, [bodily] vitamin D status, or
both.” (Lappe JM et al 2007)
(By “inversely associated”, they meant that studies consistently
link higher blood levels of vitamin
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Fish fit the
vitamin D bill; Sockeye salmon stand out
Certain fish
rank among the very few substantial food sources of vitamin D.
Among fish, wild sockeye salmon may be the richest source of
all, with a single 3.5 ounce serving surpassing the US RDA of
400 IU by about 70 percent:
Vitamin D
per 3.5 ounce serving*
Sockeye
salmon 687 IU
Albacore
tuna 544 IU
Silver
salmon 430 IU
King salmon
236 IU
Sardines
222 IU
Sablefish
169 IU
Halibut 162
IU
*For our full test
results, click
here. |
D or greater-than-average sun exposure to lower rates of
cancer.)
Americans’ vitamin D blood levels range from 50 to 140 nano-moles
per liter (nmol/L), with most positioned at the lower end of that
spectrum. Blood levels below 40 nmol/L are considered grossly
inadequate and unhealthful, and even 80 nmol/L is considered low (Lappe
JM et al 2006).
Vitamin D experts like Michael F. Holick, M.D. of Boston University
say that optimal blood levels start at 115 nmol/L, or more than
double the low end of the normal American range.
New study is second, stronger clinical trial of vitamin D versus
cancer
Only once before has the cancer-curbing potential of the
long-neglected “sunshine-and-seafood” vitamin been put to the test
in a rigorous, controlled clinical trial, in which researchers match
vitamin D against an inactive placebo pill.
This earlier trial was part of the Women’s Health Initiative (WHI),
and it had three weaknesses:
1)
The WHI study tested a much lower dose of vitamin D
(400 IU per day, versus 1,000 IU daily in the new study)
2)
Compared with the women in the new study, vitamin D
levels among women in the WHI study averaged about 40 percent lower
at the outset of the trial: specifically, 42 nano-moles per liter (nmol/L)
versus 71.8 nmol/L;
3)
The women in the WHI study did not take the prescribed
supplements nearly as consistently as those in the new study.
Despite these shortcomings, the women in the earlier WHI study who
had the highest vitamin D levels still enjoyed a reduced risk of
colon cancer.
Now, the exciting results of a small, well-designed clinical trial
bolster the WHI findings and point again to the strong
cancer-preventive potential of vitamin D.
Nebraska team delivers good vitamin D news
Last week, researchers at Creighton University in Omaha, Nebraska
reported the results of the first rigorous clinical trial to test
daily doses of vitamin D high enough to raise blood levels
substantially above the US average (i.e., to 80 nmol/L, which still
falls considerably short of optimal).
The objective of this randomized, double-blind, placebo-controlled
trial was to determine whether calcium supplements alone or
calcium plus vitamin D would reduce the risk of bone
fractures and the risk of any or all types of cancer.
They recruited 1,179 women aged 55 or older, randomly selected from
among all of the healthy post-menopausal women living in a
nine-county rural area of Nebraska.
The women were assigned to one of three groups, and were instructed
to take the pills given them every day for four years.
-
Placebo (inactive) vitamin D and calcium pills (“control” group =
288 women);
-
Calcium* plus a placebo vitamin D pill (“Calcium-Only” group = 445
women)
-
Calcium* plus 1100 IU of vitamin D3 (“Calcium + D” group =
446 women)
*1400–1500 mg of calcium citrate or carbonate, respectively.
As we noted at the beginning of this article, the results showed
that rates of cancer were 60 percent lower in the Calcium + D
group, compared with the placebo control subjects.
Vitamin D
awarded lion’s share of anti-cancer credit
But the positive
anti-cancer impact of the vitamin D-calcium combo was actually
better than it appeared at first blush.
When the
researchers excluded cancers that appeared within the first 12
months
of the study, the Calcium + D group had 77 percent fewer cancers.
(They presumed that any cancers diagnosed within the first 12 months
of the study were probably present before the study began.)
And the
researchers gave vitamin D most of the credit. While rates of
cancer were 47 percent lower in the Calcium-Only group compared with
the placebo control group, those women did no better than the
placebo control group when early-appearing cancers were excluded.
The researchers
concluded that the calcium part of the combo had little to do
with the 60 to 77 percent cancer-rate reductions seen in the Calcium
+ D group.
Vitamin D:
Choosing the ideal forms and sources
The term “vitamin
D” actually refers to either of two forms: D3 (cholecalciferol) and
D2 (ergocalciferol).
Vitamin D3, which
is more “bio-active” and effective is found in fish and other animal
foods, and is produced in skin exposed to solar UVB radiation. The
Nebraska-based researchers said that they chose vitamin D3 for this
study because it is more active and thus more effective in humans.
Vitamin D2 is a
less bio-active and beneficial form derived from plants, which
contain small amounts. However, vitamin D2 is cheaper than vitamin
D3, so most dietary supplements contain vitamin D2. Unfortunately,
most Americans get most of their vitamin D from supplements
containing this sub-optimal form (Calvo MS et al 2005).
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Japanese
women’s
bones bolstered by fish
Older
Japanese women consume very little calcium but enjoy rates of
osteoporosis 33–50 percent lower than their counterparts in the
United States and northern Europe. Japanese women eat much more
ocean fish, which are the best dietary sources of vitamin D.
Several
studies in recent years link high vitamin D intake to reduced
osteoporosis risk, probably because vitamin D helps bones retain
calcium. This may explain their greatly reduced osteoporosis
rates among Japanese women, despite calcium intakes much lower
than those found in the US or Europe.
Older Japanese
women who eat fish four times a week or more have significantly
higher vitamin D blood levels: concentrations about 10 nmol/L
higher than women who eat fish only one to three times a week
(Nakamura K et al 2000). |
Most experts
believe that the recommended daily allowance (RDA) for vitamin D
should be raised from the current 400 IU per day to 1,000 or 2,000
IU per day (Lappe JM et al 2006).
Earlier this year,
scientists who conducted a review of existing research reported that
the tolerable upper intake level for vitamin D3 should be increased
five-fold, from 2,000 International Units (IU) to 10,000 IU per day.
(See “Review
Supports Safety of Much Higher Vitamin D Intake”.)
There is also
growing evidence that higher intakes of vitamin D may be helpful in
preventing and treating diseases other than osteoporosis and cancer,
such as high blood pressure, fibromyalgia, diabetes, multiple
sclerosis, and rheumatoid arthritis.
Fishy diets
make a big “D” difference
Two years ago,
researchers at the US Food and Drug Administration and the
University of Saskatchewan penned a joint report on dietary vitamin
D, and it affirms everything we’ve said about the importance of fish
to people’s vitamin D status (Calvo MS et al 2005):
-
“The US and
Canadian populations are largely dependent on fortified foods
and dietary supplements to meet their vitamin D needs during
times of insufficient sunlight, because foods that are naturally
rich in vitamin D are not frequently consumed. … Fatty fish
represents the richest natural source of vitamin D, with salmon
being the type most commonly consumed in North America.”
-
“Liver and
other organ meats are also high in vitamin D but are not as
popular as fish and are often avoided because of their high
cholesterol content. Although mushrooms and egg yolks are listed
as sources of vitamin D, the concentrations are often very low
and variable, which results in poor documentation of the vitamin
D content of these foods.”
Sockeye salmon
offer more vitamin D than any other whole food – some 687 IU per 3.5
oz serving – thanks to their unusual diet, which features more
vitamin D-rich plankton than other salmon and most other fish.
After Sockeye, the
best vitamin D sources among our seafood selection are these (all
figures per 3.5 oz serving): Albacore Tuna (544 IU), Silver Salmon
(430 IU), King Salmon (236 IU), Sardines (222 IU), Sablefish (182 IU),
and Halibut (162 IU).
In addition, each
1000 mg capsule of our Sockeye Salmon Oil dietary supplement
contains at least 50 IU of vitamin D3.
A year before the
US-Canadian study of their citizens' vitamin D status appeared,
Danish researchers reported that diet is a significant independent
predictor of vitamin D blood levels.
They also discovered that osteoporosis rates rose sharply among
indigenous peoples living in extreme northern or southern latitudes
after switching from traditional ocean foods naturally rich in
vitamin D – primarily fish and seal/whale blubber – to Western-style
diets (Rejnmark L et al 2004).
Everyone's rightly
worried about the ill effects of global warming on the Earth's
icecaps and polar animals, but peoples native to sunlight-poor
circumpolar regions have already suffered the bad effects of
globalized junk food diets, low in vitamin D.
Sources
-
Lappe JM, Davies
KM, Travers-Gustafson D, Recker RR, Heaney RP. Vitamin D and
calcium supplementation reduces cancer risk: results of a
randomized trial. American Journal of Clinical Nutrition, Vol. 85,
No. 6, 1586-1591, June 2007
-
Lappe JM, Davies
KM, Travers-Gustafson D, Heaney RP. Vitamin D status in a rural
postmenopausal female population. J Am Coll Nutr. 2006
Oct;25(5):395-402.
-
Calvo MS,
Whiting SJ, Barton CN. Vitamin D intake: a global perspective of
current status. J Nutr. 2005 Feb;135(2):310-6. Review.
-
Nakamura K,
Nashimoto M, Hori Y, Yamamoto M. Serum 25-hydroxyvitamin D
concentrations and related dietary factors in peri- and
postmenopausal Japanese women. Am J Clin Nutr. 2000
May;71(5):1161-5.
-
Rejnmark L,
Jorgensen ME, Pedersen MB, Hansen JC, Heickendorff L, Lauridsen
AL, Mulvad G, Siggaard C, Skjoldborg H, Sorensen TB, Pedersen EB,
Mosekilde L. Vitamin D insufficiency in Greenlanders on a
westernized fare: ethnic differences in calcitropic hormones
between Greenlanders and Danes. Calcif Tissue Int. 2004
Mar;74(3):255-63. Epub 2003 Dec 23.
