"Do Vitamin D Supplements Reduce the Risk of Dying from Cancer?"
It all started with this famous study published in 1980.
Johns Hopkins researchers were trying to figure out why states
like New Mexico and Arizona have only about half the colon cancer rates
of states like New York, New Hampshire, and Vermont.
Maybe it's because they got so much sun.
And so they proposed that maybe the sunshine vitamin, vitamin D,
is a protective factor against colon cancer.
Since then, sun exposure has been associated
with lower rates of 14 other types of cancer too.
Vitamin D may also affect cancer survival.
Higher blood levels of vitamin D were associated
with lower mortality of patients with colorectal cancer.
How much lower? Like nearly half the mortality.
And the higher the D levels, the lower the death rate appeared to fall.
This may explain why the survival rate from colon cancer
may depend in part on the season of diagnosis---
the reason the risk of a rapid death is lowest if you're diagnosed in the fall,
after you've spent the summer building up your vitamin D stores.
But look, there are other risk factors that could be seasonal too.
Maybe people are taking advantage of the fall harvest and eating healthier.
Maybe that's why the lower risk in the fall season.
Or maybe there's more drinking in the winter.
And in the summer running around outside,
not only are you getting more sun, you're running around outside,
getting more exercise, which may itself be protective.
So these kinds of studies just provide circumstantial evidence.
Establishing a cause and effect relationship
between colon cancer and vitamin D deficiency
using observational studies is challenging
because of confounding factors like the exercise,
so-called lurking variables.
For example, there may be tight correlation between ice cream sales
and drowning deaths, but that doesn't mean ice cream causes drowning.
A more likely explanation is that there is a lurking third variable like hot weather,
summertime, that explains why drowning deaths are highest
when ice cream consumption is highest.
That's kind of a trivial example,
but this actually happened with hormone replacement therapy.
Women taking drugs like Premarin appeared to have 50% less risk
of heart disease, and so doctors prescribed it to women by the millions.
But if you dig a little deeper into the data, yes, women taking estrogen
had 50% lower risk of dying from heart disease, but they also had
a 50% lower risk of dying from accidents and homicide,
so it probably wasn't the drug.
See, the only way to know for sure is to put it to the test in a randomized clinical
trial, where you give half the women the drug and see what happens.
And a decade later they did, and instead of having a 50% drop in risk,
within a year of being given the hormone pills, heart attack and death rates shot up 50%.
In retrospect the lurking variable was likely socioeconomic class.
Poor women are less likely to be prescribed hormone replacement therapy,
and more likely to be murdered and die of heart disease.
Because of the lurking variable, a drug we now know to be dangerous
had appeared to be protective.
Besides lurking variables, there's also the possibility of reverse causation.
Maybe low vitamin D levels didn't worsen the cancer;
maybe the cancer worsened the vitamin D levels.
This may be unlikely since tumors don't appear to directly affect vitamin D levels,
but cancer treatment might.
Even simple knee surgery can dramatically drop vitamin D levels
within hours, thought to be because of just the inflammatory insult
of cutting into somebody.
So maybe that could help explain the link between lower D and lower survival.
And hey, if you've got cancer, maybe you're spending
less time running around at the beach.
So yes, higher vitamin D levels are associated
with improved survival in colorectal cancer, and in breast cancer—
in fact, about double the risk of breast cancer recurrence and death
in women with the lowest vitamin D levels.
And vitamin D levels are also associated with longer survival with ovarian cancer,
and other cancers like lymphoma,
but bottom line, as we learned with hormone replacement,
is that you have to put it to the test.
But there weren't a lot of randomized controlled trials
on vitamin D supplements and cancer until now.
We now have a few randomized controlled trials,
and vitamin D supplements do indeed appear
to reduce the risk of dying from cancer. What dose?
The researchers suggest maybe getting blood levels up to at least
around 75 nanomoles per liter,
levels not reached by as many as three quarters of women with breast cancer,
or a striking 97% of colon cancer patients.
Getting up to those kinds of levels, 75 or perhaps even better 100,
might require about 2- to 4000 international units of vitamin D a day,
levels of intake for which there appear to be no credible evidence of harm.
Regardless of what the exact level is, the findings of these kind of studies
may have a profound influence on future cancer treatment.