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Vitamin D and
Cancer: What Do Researchers See?
Vitamin D has been getting more
attention for its potential role in reducing cancer risk. In
fact, it was a major topic of discussion at the American Institute
for Cancer Research’s (AICR) recent conference on food,
nutrition, physical activity and cancer. While there is not yet
a global consensus on its role in protection, the nation’s
top cancer researchers have a lot to say about the sunshine vitamin.
For some time, laboratory studies
have shown that vitamin D helps maintain control of cell growth.
At the AICR conference, evidence was shared that confirms vitamin
D can help activate certain proteins that suppress tumor growth
and development.
The question of how much D continues
to be debated. Some research now suggests that the current recommended
intake level (400 International Units (IU) daily for most adults)
may not be enough to raise blood levels of the vitamin to levels
associated with lower cancer risk. |
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Further complicating the issue
are concerns about how to best evaluate vitamin D status. Simply
documenting how much vitamin D someone gets from diet or supplements
is inadequate because we also produce our own vitamin D in response
to sunlight. Calculating the amount produced following sun exposure
is also difficult, as age, skin color and environmental pollution
can all affect vitamin production.
Experts tend to agree that the
best way to assess someone’s vitamin D status is to measure
blood levels. Unfortunately, accurate and reliable methods are
not widely available. Furthermore, an optimal blood level for
the vitamin is not yet clear. Many researchers seem convinced
that levels currently thought of as "normal" may not
be high enough to encourage optimal bone health or reduced cancer
risk. Shockingly, if the highest proposed blood levels of vitamin
D are adopted, 50 to 78 percent of Americans will be classified
as having low levels of the vitamin.
Despite the wealth of evidence
suggesting a link between vitamin D and cancer protection, not
all studies reveal a benefit with increased vitamin D intake.
Take, for example, the recently published data from the Women’s
Health Initiative that failed to show lower breast cancer risk
among women who received 1000 milligrams (mg) calcium plus 400
IUs vitamin D daily. Although the women were followed for seven
years, some experts suggest that it is too soon to see an impact,
as part of vitamin D’s purported effect occurs early in
the cancer process, which can take 20 years to develop. Longer
follow-up may tell us more.
The research suggests that vitamin
D has great potential as one part of a strategy to lower cancer
risk. For some of us, boosting intake to the top of the safety
margin – about 1000 to 2000 IU per day – may be needed
for lower cancer risk. Many experts urge boosting intake now,
but others are calling for more evidence before recommending
higher intake levels, especially if any genetic differences could
put some people at risk. |
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