Vitamin D and breast cancer

[Guest guest]

Vitamin D from supplements may reduce the risk for breast cancer in women

with relatively low vitamin D intakes, suggest study findings published

online April 14 ahead of print in the *American Journal of Clinical

Nutrition*. The study also found a significant inverse trend for higher

calcium intakes but no interaction between vitamin D and calcium. However,

no associations were found between overall combined vitamin D or calcium

intakes from food and supplements and breast cancer risk.

It is unclear whether the possible association between dietary vitamin D and

reduced breast cancer risk is confounded or modified by calcium and vice

versa, N. , from Population Studies and Surveillance, Cancer

Care Ontario, in Toronto, Canada, and colleagues note in their article. It

is also unclear whether the association between dietary vitamin D and breast

cancer differs by menopausal status.

To investigate these uncertainties, the researchers used the Ontario Cancer

Registry to identify 3101 women aged 25 to 74 years diagnosed between June

2002 and April 2003 with a first pathologically confirmed breast tumor (case

patients). The researchers used random-digit dialing methods to identify

3471 matched women without breast cancer (control subjects). All of the

women completed an epidemiologic questionnaire and a modified Block food

frequency questionnaire that measured 178 foods and supplements.

Supplemental vitamin D at more than 10 µg/day (400 IU/day) vs no

supplemental vitamin D was associated with a reduced risk for breast cancer

(adjusted odds ratio [OR], 0.76; 95% confidence interval [CI], 0.59 - 0.98).

However, no dose-response relationship was observed.

The study authors note that the mean intake of vitamin D in study subjects

was low. Only 13% of case patients and 14% of control subject reported using

single-product vitamin D supplements or cod liver oil. No associations were

evident between total combined vitamin D intake or vitamin D intake from

foods alone and breast cancer risk.

In addition, there were no statistically significant associations between

calcium intake from foods, supplements, or total combined intake and breast

cancer risk; however, a significant inverse trend was noted across

categories of calcium supplement use (*P* for trend = .04). Calcium

supplement use was more common in study participants than was vitamin D

supplement use; 33% of case patients and 35% of control subjects took

calcium.

Moreover, the results " do not suggest an interaction between calcium and

vitamin D intakes, and these 2 variables did not confound each other, "

according to the researchers. There were also no significant interactions

between vitamin D, calcium, or menopausal status, and multivitamin use was

not associated with breast cancer risk.

The study authors point out that measuring vitamin D or calcium from foods

as opposed to supplements may be more prone to misclassification

(potentially biasing results toward the null). It is also possible that

foods containing vitamin D and calcium contain other detrimental components

that counteract the potential benefits from vitamin D, such as dietary fat

in milk. Furthermore, the possibility that the observed associations were

the result of chance or residual confounding cannot be ruled out; however,

the finding that multivitamin use was not associated with breast cancer risk

suggests that the associations are not because of residual confounding by

other unmeasured healthy lifestyle traits among supplement users.

Strengths of the study, the authors say, include its large sample size,

population-based recruitment of case patients and control subjects, and high

response rates.

Limitations of the study include observational design, possible

misclassification of measurement of vitamin D or calcium from foods vs

supplements, and possible chance results or residual confounding.

" Further research is needed to investigate the effects of higher doses of

vitamin D and calcium supplements, " the researchers conclude.

*The study authors have disclosed no relevant financial relationships.*

*Am J Clin Nutr.* Published online April 14, 2010.

www.medscape.com

--

Ortiz, MS, RD

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