Will eating nuts save your life?

One of the more eye-catching ways to promote a food or a medicine is to calculate the total reduction in deaths among those consuming the wonder product. 

Statistician Andrew Gelman blogs:

Jeff sent me an email with the above title and a link to a press release, “Nut consumption reduces risk of death,” which begins: 

According to the largest study of its kind, people who ate a daily handful of nuts were 20 percent less likely to die from any cause over a 30-year period than those who didn’t consume nuts . . . Their report, published in the New England Journal of Medicine, contains further good news: The regular nut-eaters were found to be more slender than those who didn’t eat nuts, a finding that should alleviate fears that eating a lot of nuts will lead to overweight. . . . 

For the new research, the scientists were able to tap databases from two well-known, ongoing observational studies that collect data on diet and other lifestyle factors and various health outcomes. The Nurses’ Health Study provided data on 76,464 women between 1980 and 2010, and the Health Professionals’ Follow-Up Study yielded data on 42,498 men from 1986 to 2010. . . . 

Sophisticated data analysis methods were used to rule out other factors that might have accounted for the mortality benefits. For example, the researchers found that individuals who ate more nuts were leaner, less likely to smoke, and more likely to exercise, use multivitamin supplements, consume more fruits and vegetables, and drink more alcohol. However, analysis was able to isolate the association between nuts and mortality independently of these other factors. . . . 

The authors noted that this large study cannot definitively prove cause and effect; nonetheless, the findings are strongly consistent with “a wealth of existing observational and clinical trial data to support health benefits of nut consumption on many chronic diseases.” . . . 

The study was supported by National Institutes of Health and a research grant from the International Tree Nut Council Nutrition Research & Education Foundation. 

The press release did not link to the study—what’s with that, anyway, how hard would it be to include a link???—but a quick google led to this article, “Association of nut consumption with total and cause-specific mortality,” by Ying Bao, Jiali Han, Frank Hu, Edward Giovannucci, Meir Stampfer, Walter Willett, and Charles Fuchs.

Similarly, back in the mid-1990s, my doctor said my cholesterol was too high so I should take a statin. An affable detail man had just given him a box of free Mevacor pills. (Mevacor had been the first statin on the market when introduced in 1987.) So my doctor gave me a fistful and wrote a prescription. But I looked up statins on the new-fangled Internet and found that the hot new statin was Lipitor, which went on to become the biggest moneymaking pill in the world in the 2000s.

The most striking Lipitor study was one from Scandinavia that showed that among middle-aged men over a 5-year-period, the test group who took Lipitor had a 30% lower overall death rate than the control group. Unlike the nuts study, this was an actual experiment.

That seemed awfully convincing, but now it just seems too good to be true. A lot of those middle-aged deaths that didn't happen to the Lipitor takers didn't have much of anything to do with long-term blood chemistry, but were things like not driving your Saab into a fjord. How does Lipitor make you a safer driver? 

I sort of presumed at the time that if they had taken out the noisy random deaths, that would have made the Lipitor Effect even more noticeable. But, of course, that's naive. The good folks at Pfizer would have made sure that calculation was tried, so I'm guessing that it came out in the opposite direction of the one I had assumed: the more types of death included, the better Lipitor looks. Apparently, guys who took Lipitor everyday for five years were also good about not driving into fjords and not playing golf during lighting storms and not getting shot by the rare jealous Nordic husband or whatever. Perhaps it was easier to stay in the control group than in the test group?

Here’s how I would approach claims of massive reductions in overall deaths from consuming some food or medicine:

Rank order the causes of death by how plausible it is that they are that they are linked to the food or medicine. For example:

1. Diabetes

2. Heart attacks

3. Strokes

4. Cancer

5. Genetic diseases

6. Car accidents

7. Drug overdoses

8. Homicides

9. Lightning strikes

If this nuts-save-your-life finding is valid, then the greater effects should be found in causes of death near the top of the list (e.g., diabetes). But if it turns out that eating nuts only slightly reduces your chances of death from diabetes but makes you vastly less likely to be struck by lighting, then we’ve probably gotten a selection effect in which nut eaters are more careful people in general and thus don’t play golf during thunderstorms, or whatever.