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Al Pater posted study [1] to the CR email list (thanks Al), that was a meta-analysis of studies of the relationship between vitamin intake and stomach (gastric) cancer risk. It found that several vitamins, including Vitamin A, C and E, in modest doses, could indeed reduce the risk of stomach cancer by about 25%. But high doses of those same vitamins resulted in an increased risk of almost the same magnitude. They also observed that modest doses of these vitamins were only beneficial for gastric cancer when they came from food (plants or animals) - vitamin supplements showed no such benefits. The authors speculate that the reason could be differences in bioavailability of vitamins from foods vs. pills:

 

The current study also draws attention to the fact that vitamins from food
(plant or animal) contribute more to reductions in GC risk than synthetic vitamin
supplements. Some investigators have noted that the bioavailability of vitamins
differs depending on whether the vitamin comes from food or is synthetic, which
could explain the results. For example, Carr reported differences in bioavailability
between synthetic and kiwifruit-derived vitamin C in a randomized crossover
pharmacokinetic study [ref].

 

But it seems at least as plausible to me that the benefits come not just from these specific vitamins (heck, in the case of vitamin E alone there is really a whole family of vitamins rather than just a single vitamin E), but from the many beneficial phytochemicals in foods, for which these three vitamins are merely markers.

 

--Dean

 

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[1] Vitamin intake reduce the risk of gastric cancer: meta-analysis and systematic review of randomized and observational studies.

Kong P, Cai Q, Geng Q, Wang J, Lan Y, Zhan Y, Xu D.
PLoS One. 2014 Dec 30;9(12):e116060. doi: 10.1371/journal.pone.0116060. eCollection 2014. Review.
PMID: 25549091 Free PMC Article
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4280145/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4280145/pdf/pone.0116060.pdf

Abstract

AIM:

The association between vitamin intake and gastric cancer (GC) has been widely debated due to the relatively weak evidence. In this study, a meta-analysis of prospective and well designed observational studies were performed to explore this association.

METHODS:

MEDLINE, Cochrane Library, and Sciencedirect were searched for studies of vitamin consumption and gastric cancer. This produced 47 relevant studies covering 1,221,392 human subjects. Random effects models were used to estimate summary relative risk (RR). Dose-response, subgroup, sensitivity, meta-regression, and publication bias analyses were conducted.

RESULTS:

The RR of gastric cancer in the group with the highest vitamin intake was compared to that of the lowest intake group. Total vitamin intake was 0.78 (95% CI, 0.71-0.83). In 9 studies that individuals were given doses at least 4 times above the tolerable upper intake (UL) vitamins, the RR was 1.20 (95% CI, 0.99-1.44). However, in 17 studies that individuals received doses below the UL, the RR was 0.76 (95% CI, 0.68-0.86). Dose-response analysis was conducted on different increments in different types of vitamins (vitamin A: 1.5 mg/day, vitamin C: 100 mg/day, vitamin E: 10 mg/day) intake with a significant reduction in the risk of gastric cancer, respectively, 29% in vitamin A, 26% in vitamin C, and 24% in vitamin E.

CONCLUSION:

This meta-analysis clearly demonstrated that low doses of vitamins can significantly reduce the risk of GC, especially vitamin A, vitamin C, vitamin E.

Table 2. Subgroup analyses of vitamins intake and gastric cancer Risk.
Heterogeneity test
------------------------------------
Group NO. of reports RR (95%) Chi^2 P(I^2)
------------------------------------\
Vitamin source
plant 15 0.79(0.69,0.89) 36.96 0.002 65
animal 11 0.78(0.68,0.89) 25.93 0.0003 61
drug supplement 16 0.95(0.80,1.13) 33.09 0.58 55

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Thanks for that heads-up.  Good idea to do whatever we can to avoid stomach cancer.  That said, it may be relevant that deaths rates from stomach cancer are several multiples greater in China and Japan than in the USA.  And stroke is the leading cause of death in China.  There is good reason to suspect these are connected.  And the connection is salt.  Another good way to avoid stomach cancer (and stroke) is to eat a lot less salt than the average intakes in China and Japan.  (Ever notice how thirsty you are after eating chinese or japanese food?) 

 

Yet, while the death rate from stoke is huge, death from CHD is almost negligible in China and Japan.  So, while stroke and CHD are both diseases of the circulatory system, it is pretty clear they have quite different causes.  I, of course, am not a fanatic about salt restriction, because it seems clear there are quite serious risks associated with too little of it.  But enough to make you seriously thirsty after a meal on a regular basis is probably enough to substantially raise your risk of both stomach cancer and stroke.

 

Rodney.

 

=============

 

"The unverified conventional wisdom is almost invariably mistaken."

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