Vitamins reduce gastric cancer risk, but don’t forget your fruits and veggies!

I have a friend that once ate nearly half a bottle of adult gummy multivitamins because they were essentially gummy bears, and how could gummy bears hurt anyone? Thankfully, all was ok, but this highlights an overarching debate over the risks and benefits of multivitamins and vitamin or other over the counter supplement. One problem with any over the counter vitamin or supplement is the lack of Food and Drug Association (FDA) evaluation and approval of the contents or statements made on the label of such products. You think you could be getting high-quality Vitamin D3, but be getting powdered pencil shavings stuffed in a capsule. Seriously. Though there are obviously more reliable commercial sources of vitamins and supplements than others, this lack of protective oversight has limited research and the overall medical community’s enthusiasm for endorsing certain products for patient use. This is not to say research on vitamin intake has not been performed, as many studies on specific vitamin effects in various human diseases and conditions exist in the scientific literature. In fact, some researchers consider certain vitamins and supplements, should be considered pharmaceuticals and be labeled accordingly due to potential toxicity and overdose side effects. Again, this requires FDA oversight

With this said, there is evidence for therapeutic benefits for regular intake of over-the-counter vitamins, and one recent study by Kong et al. (Dec. 2014, Vitamin Intake Reduce the Risk of Gastric Cancer: Meta-Analysis and Systematic Review of Randomized and Observational Studies. PLoS ONE 9(12): e116060) showed that intake of vitamins reduced risk of developing gastric cancer. The study was a retrospective systematic review and analysis of published clinical studies including a wide variation of patients of different ethnic backgrounds, ages, and times they were followed. Ultimately, 47 studies and over 1,000,000 subjects were included in the analysis. Data assessed from the studies included study design, location, subject age, gender, study period, control subjects in case-control studies, sample size, types of vitamins assessed and intake method used in the study. Other factors such as whether studies were blinded (keeping doctors and patients in the dark about treatments to reduce bias) quality of the methods, and other concerning sources of bias were taken into consideration in this study. You have to pay attention to all of these factors, as patients and researchers have a good way of convincing themselves of things they may believe to be true, whether they are or not.

As an aside: For your benefit, when reading a study look to see if the analyses (or at least some) were blinded, there are good controls (placebo treatments) or other control which should have no effect (negative control) and sometimes positive controls (where a desired effect is expected for comparison) are used. These can help you interpret the validity of the study, the data collected, and discussion and statements made about the data from the study. Sometimes even the statistical tests used may be inappropriate, but even scientists do not know which stats should be used in all scenarios. Bottom line, be aware and be educated. This work is to help the people, in principle, and we are the people.
At any rate, this study seems to be solidly constructed, but has some limitations as almost all studies do. Interestingly, 29 of the 47 studies should an inverse association between the amount of vitamins (general) and the risk of developing gastric cancer. In other words, taking vitamins = less gastric cancer. For dose-response of independent vitamins, 1.5 mg/day Vitamin A, 100 mg/day Vitamin C, and 10 mg/day Vitamin E were linked to a significantly reduced risk of gastric cancer development (36% reduction for Vitamin A, 35% for Vitamin C, and 32% reduction for Vitamin E). These are not super-high amounts, in fact they are relatively low, but still the reduced gastric cancer risk is there.

A key finding from the analysis was that Vitamins FROM FOOD (veggies and animal sources) reduce the risk better than synthetic supplemental vitamins. I think this is quite logical, and matches well with the dosing from the studies that seemed to lower risk. The authors refer to suggestions from others that bioavailability is different between food sources and supplemental sources, which might account for this finding. Vitamins A, B, C, and E all seemed to lower risk of gastric cancer, but not Vitamin D. The study only included 5 case controlled studies for analysis, so the information may have been limited for a firm conclusion.

The authors state the strengths of the study are its large analyzed patient population and this is the first study like this to find a dose-dependent relationship between these vitamins and gastric cancer risk. Limitations highlighted are the variable study populations and time periods and flawed design of some of the studies analyzed. In this sort of analysis, it is hard to control for everything, and I think the strengths outweigh the weaknesses presented in this study.

So what are the take-aways from this article? Low doses of vitamins can lower risk of gastric cancer, and that food sources of these vitamins may be better at this than dietary supplements like multivitamins. The dosing emphasized from the analysis is consistent with what you might get from food items, so this is reasonable. Also, fruits and vegetable intake has been linked to reduced gastric cancer risk, so this strengthens the case.The FDA has approved food intake, assuming from the need to eat to survive, which is a plus based on the findings of this study. Basically, no need to worry about whether you getting the right vitamins (or vitamins at all) from supplements if you want to reduce gastric cancer risk. So go out and buy a bunch of colorful fruits and veggies, balance your diet well to reduce risk of other health issues, exercise, and you will be on your way to a you with lowered risk of gastric cancer and perhaps other types of cancer. Hats off to Kong and colleagues for this interesting and well-done study.