Do vegetarians live longer?

On 2nd February 2017, Melody Ding, a senior researcher from the University of Sydney published an article in The Conversation titled “Do vegetarians live longer? Probably, but not because they’re vegetarian”.[1] Her preferences were revealed early in the article when she writes, “vegetarianism and its more austere cousin, veganism, are becoming increasingly popular”. A person calling a vegan diet austere does not know how to cook.

Ding also states that there are several studies relating to diet and longevity but the results are mixed. She quotes one study that followed more than 95,000 men and women in the United States from 2002 to 2009, found vegetarians had a 12% lower risk of death from all causes than non-vegetarians.[2] This study used data from Adventist Health Studies.

The Orlich paper that Ding refers to classifies the diet into five categories.

Category%BMI
Vegan
No red meat, fish, poultry, dairy, eggs
4.223.6
Lacto-ovo vegetarians
Vegan with eggs and milk
31.625.7
Pesco-vegetarians
Vegan with fish, milk and eggs
11.426.3
Semi-vegetarians
Red meat, poultry less than once a week plus fish, milk, and eggs
6.127.3
Non-vegetarians
Red meat, poultry more than once a week plus fish, milk, and eggs
46.828.8

It appears that Ding groups the vegan, lacto-ovo-vegetarians and pesco-vegetarians into a vegetarian group.

It is important to note that even non-vegetarian Seventh-day Adventists are much healthier that the average American so the statement that “vegetarians had a 12% lower risk of death from all causes than non-vegetarians” needs to be interpreted as “vegan, lacto-ovo-vegetarians and pesco-vegetarians have a 12% lower risk of death from all causes than omnivore Seventh-day Adventists who are much healthier than the average American”.

The Adventist Health Study 1 (AHS-1) study showed 30-year-old Adventist males lives 7.3 years longer than the average 30-year-old white Californian male and with females living 4.4 years longer than the average Californian white female. For vegetarians (including fish, eggs and dairy), it is 9.5 years longer for men and 6.1 years longer for women.[3] Note that Californians are much healthier than the average American, being in the top five states for longevity. Also Hispanics and Asians have longer life expectancies than white Americans who have longer life expectancies than black or native Americans.


The paper that The Conversation article refers to is a 2015 paper[4] from the University of Sydney that uses data from the 45 and Up study. The paper identifies several limitations of the study such as:

  • Self-reporting of the data
  • Sampling methodology
  • The six risk factors measured (poor diet, high alcohol intake, physical inactivity, prolonged sitting, long sleep duration, short sleep duration) were only given a positive or negative response. That is, the measured behaviour was risky or it was not.

Of far greater concern is the measurement of what constitutes a risky behaviour when it comes to diet. Given that 83% of the participants were considered to have a healthy dietary behaviour, it is difficult to understand why 37% of the participants were considered to be overweight and 20% obese.

Given that only less than 10% of middle-age women and approximately 5% of middle-age men are considered to be low risk for heart disease[5], it appears somewhat optimistic for the paper to conclude that 31.2% of the study participants have no risk factors—especially given (once again) that 37% of the participants are overweight.


The Conversation article states,

In most previous studies, vegetarians did have lower risk of early death from all causes in unadjusted analysis. However, after controlling for other lifestyle factors, such as the ones listed above, the risk reduction often decreased significantly (or even completely vanished).

The lifestyle factors that were removed from the analysis included overweight & obesity and physical activity. These factors are not independent of diet. Seventh-day Adventists studies (and many others) have shown that the more vegetarian the diet, the lower the BMI and the more physical activity people (and rats) are inclined to undertake.

It appears that vegan Seventh-day Adventists of California are the healthiest group of people on the planet, out-performing even the Japanese or the Okinawan people.

The conclusion of The Conversation article is:

Put more simply, when we crunched the data we found vegetarians did not have a lower risk of early death compared with their meat-eating counterparts.

This is reminiscent of Jacob Yerushalmy’s disagreement with researchers who claimed that women who smoked had lower birth-weight infants.[6] He suggested that smoking was not the cause of the lower birth weight but a result of “mode of life” differences between the smoking population and non-smoking population.

Headlines such as “Do vegetarians live longer? Probably, but not because they’re vegetarian” make the news because people wish to have reasons to continue their current unhealthy dietary habits – not because they contribute to the health of our nation.

As Eric Rimm (the well-known Harvard epidemiologist) stated,

We can’t tell people to stop eating all meat and all dairy products. Well, we could tell people to become vegetarians. If we were truly basing this only on science, we would, but it is a bit extreme.[7]

Footnotes

  1. Ding, M. (2017) Do vegetarians life longer? The Conversation. [online]. Available from: http://theconversation.com/do-vegetarians-live-longer-probably-but-not-because-theyre-vegetarian-72191.
  2. Orlich, M. J. et al. (2013) Vegetarian Dietary Patterns and Mortality in Adventist Health Study 2. JAMA Internal Medicine. 173 (13), 1230.
  3. Fraser, G. E. & Shavlik, D. J. (2001) Ten Years of Life – Is It a Matter of Choice? Archives of Internal Medicine. 161 (13), 1645–1652.
  4. Ding, M. et al. (2015) Traditional and Emerging Lifestyle Risk Behaviors and All-Cause Mortality in Middle Aged and Older Adults: Evidence from a Large Population-Based Australian Cohort. PLOS Medicine. 12 (12), 1–21.
  5. Stamler, J. et al. (2005) ‘Current status: six established major risk factors—and low risk’, in M. Marmot & P. Elliot (eds.) Coronary Heart Disease Epidemiology: From aetiology to public health. Second Edition Oxford University Press. pp. 32–70.
  6. Parascandola, M. (2014) Birthweight and mortality: Jacob Yerushalmy on self-selection and the pitfalls of causal inference. International Journal of Epidemiology. [Online] 43 (5), 1373–1377.
  7. Fox, M. (2002) Trans-fat increase cholesterol levels [online]. Available from: http://jawawa.id/index.php/newsitem/trans-fat-increase-cholesterol-levels-1447893297 (Accessed 29 March 2017).

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