Cancer Benefit of Vitamin D May Be Limited to Colon Cancer

[Guest guest]

Cancer Benefit of Vitamin D May Be Limited to Colon Cancer

By Bankhead, Staff Writer, MedPage Today

Reviewed by Zalman S. Agus, MD; Emeritus Professor at the University

of Pennsylvania School of Medicine.

October 30, 2007

MedPage Today Action Points

* Explain to interested patients that this study suggests that

there may be an association of higher levels of 25-hydroxyvitamin D

with reduced risk of colon cancer mortality but not with mortality

from other types of cancer.

* Note that the findings came from a review of a large database,

not a randomized, controlled clinical trial and cannot determine

causality.

Review

BETHESDA, Md., Oct. 30 -- Vitamin D levels do not appear to protect

against cancer, with the possible exception of colorectal disease,

according to data from a nationwide study.

The analysis failed to show an association between baseline vitamin D

status and overall cancer risk in men, women, or in various racial,

ethnic or age groups, Michal Freedman, Ph.D., of the National Cancer

Institute, and colleagues, reported in the Nov. 7 issue of the Journal

of the National Cancer Institute.

However, individuals with baseline serum levels of 25-hydroxyvitamin D

of 80 nmol/L or higher did have a 72% (95% confidence interval = 32%

to 89%) lower risk of colorectal cancer compared with people who had

lower serum levels of vitamin D (lower than 50 nmol/L; P=0.02 for the

trend).

The investigators left the door open, though, for continued

investigation of associations between the vitamin and cancer risk.

" Additional studies with large numbers of samples of measured 25(OH)D

serum levels, preferably at multiple time points, are needed to

confirm the total cancer mortality findings of this paper and to

obtain more accurate risk estimates for mortality from specific

cancers, " they concluded.

A variety of preclinical and epidemiologic evidence has suggested that

increased intake or endogenous production of vitamin D is associated

with reduced cancer risk. In vitro studies have shown that vitamin D

reduces cell proliferation, and stimulates apoptosis and cell

differentiation, the authors noted.

Ecologic and observational studies have demonstrated an inverse

association between residential exposure to ultraviolet radiation (the

principal source of naturally occurring vitamin D) and cancer

mortality. However, the association between vitamin D and cancer risk

and mortality had not been evaluated prospectively.

So Dr. Freedman and colleagues reviewed data from the Third National

Health and Nutrition Examination Survey. They focused on 16,818 adult

participants who completed the NHANES physical examination from 1988

through 1994 with measurement of serum 25(OH)D. Follow-up from data

collection continued until Dec. 31, 2000.

Baseline data showed that men, whites, and better-educated individuals

had significantly higher serum levels of 25(OH)D.

Increasing body mass index was associated with decreasing levels of

25(OH)D, but increasing physical activity was associated with higher

levels.

Dietary vitamin D and calcium and serum retinol were higher in

participants who had higher 25(OH)D levels.

The investigators identified 536 cancer deaths in 146,578

person-years. Analysis of season/latitude subpopulations revealed no

association between cancer mortality and winter/lower latitude or

summer/higher latitude groups. Extensive subgroup analysis failed to

reveal any significant associations between 25(OH)D levels and overall

cancer mortality.

Analysis of the relationship between serum 25(OH)D and site-specific

cancer mortality revealed no association with lung cancer,

non-colorectal digestive cancers, breast cancer, prostate cancer,

lymphoma or leukemia, or the category of " other " cancers.

In an editorial that accompanied the article, Johanna T. Dwyer, D.Sc.,

and D. , Ph.D., of the National Institutes of Health,

emphasized the complicated nature of the relationship between

nutritional factors and cancer.

" These findings must be put into the context of total diet and

lifestyle, " they wrote. " While vitamin D may well have multiple

benefits beyond [strengthening] bone, health professionals and the

public should not in a rush to judgment assume that vitamin D is a

magic bullet and consume high amounts of vitamin D, " they continued.

" More definitive data on both benefits and potential adverse effects

of high doses are urgently needed. "

The editorialists noted some limitations with the use of the NHANES

III cohort. " NHANES III was a cross-sectional study that identified

associations but not causation, " they said.

They also pointed out that residual confounding is a particular

problem because peculiarities in NHANES sampling may have affected

both measures of vitamin D exposure and outcomes. For instance, season

and latitude, both related to 25(OH)D levels, were linked in the dataset.

Furthermore, they noted, the fact that 25(OH)D levels were measured

only at one point in time means they would not represent long-term

levels. " Nor would they reflect the nadir of 25(OH)D reached during

the year. There also might be fewer lower 25(OH)D levels in the

summer/higher latitude sample than would be the case if all subjects

had been examined in the winter. This is a cause of concern because in

Norway the maximal level of 25(OH)D is reached between the months of

July and September and it is 20% - 120% higher than the corresponding

winter value, suggesting that season of diagnosis is a predictor of

colon cancer survival. "

The authors of the study and editorial had no disclosures. The study

was supported by the National Cancer Institute.

Additional source: Journal of the National Cancer Institute

Source reference:

Freedman DM, et al " Prospective study of serum vitamin D and cancer

mortality in the United States " J Natl Cancer Inst 2007; 99: 1594-1602.

Additional source: Journal of the National Cancer Institute

Source reference:

CD, Dwyer JT, " The 'sunshine vitamin': benefits beyond bone? " J

Natl Cancer Inst 2007; 99: 1563-1565.