- FRIDAY, May 16 (HealthDay News) — Women with breast cancer who have a
vitamin D deficiency at the time of diagnosis are more likely to have a
recurrence or to die from their disease, a new study shows.

Surprisingly, the researchers also found that only 24 percent of the
patients had adequate levels of vitamin D when they were diagnosed.

“This study found that vitamin D deficiency is very common among women
with breast cancer, and it suggests that vitamin D deficiency is linked to
poorer outcomes in these women,” Dr. Nancy Davidson, director of the
breast cancer program at the Johns Hopkins Kimmel Cancer Center, said
during a May 6 press conference. Davidson is president of the American
Society of Clinical Oncology (ASCO).

Nevertheless, the evidence isn't strong enough to suggest women with
breast cancer take more of the vitamin.

“It's premature to tell all women diagnosed with breast cancer that
they should take vitamin D supplements over and above what's recommended
for bone health,” said study author Dr. Pamela Goodwin, a medical
oncologist with Mount Sinai Hospital and a professor of medicine at the
University of Toronto. “If you're a woman with breast cancer, it's
probably worthwhile having vitamin D levels checked. If they're deficient,
they should take more to get it in the range that we think is
beneficial.”

The optimal levels of vitamin D associated with breast cancer risk in
this study do overlap with optimal levels for bone health, Goodwin
added.

Prior research has suggested that vitamin D levels may be associated
with breast cancer risk, an idea that is biologically plausible.

“We know from basic science studies that breast cancer cells have
vitamin D receptors and can interact with vitamin D,” explained Goodwin,
who plans to present her findings at the ASCO annual meeting, being held
from May 31-June 3, in Chicago.

There is, however, a lot of confusion about the different health
benefits of vitamin D and, the authors said, daily allowance
recommendations vary greatly around the world.

The study involved 512 women newly diagnosed with localized breast
cancer (confined to the breast and arm pit) between 1989 and 1995. All
participants had had blood taken at the time of diagnosis and had also
filled out a questionnaire on diet. Vitamin D levels were measured by
radioimmunoassay.

The women, whose age averaged about 50, were followed for just under 12
years. Of the total, 37.5 percent were deficient in vitamin D (the lowest
levels), 38.5 percent had insufficient levels of vitamin D (not deficient
but not quite healthy levels), and 24 percent had levels in the healthy
range.

Women who were premenopausal, weighed more, had high insulin levels and
had more aggressive tumors were all more likely to have low vitamin D
levels.

“Fat tissue acts as a trap for vitamin D,” Goodwin explained. “Levels
were also lower in younger women, which was a bit of a surprise, until we
realized older women were taking more supplements.”

The risk of breast cancer spreading was almost double in women with
deficient levels of vitamin D at diagnosis, compared with women whose
levels were healthy, the researchers said.

The risk of dying of breast cancer was 75 percent higher in women with
too-low levels of vitamin D versus women in the optimal range, they
added.

However, there was no survival difference between women with
healthy levels and insufficient levels. The data also suggested that there
may be a small increased risk of metastasis or death if vitamin D levels
are high, but not a statistically significant effect, Goodwin said.

“This suggests that there's a healthy level for vitamin D and, if you
are deficient, you have an increased risk of metastasis, but if you go
above [a certain point], your risk of death goes up again,” Goodwin
said.

Although it's not a firm conclusion, Goodwin added, the finding “is
raising a red flag. It's probably not safe to take very high levels and
get vitamin D levels up really high.”

And the findings are consistent with another study which found that men
with prostate cancer who took vitamin D died earlier than those taking a
placebo.

More information

The American Society of Clinical Oncology has more
information on breast cancer.