Vegetarians Live Longer and Healthier

An online published paper out in June 2013, designed as a large prospective study found that people who followed a vegetarian diet had a lower risk for death from any cause, and men in particular also saw benefits for cardiovascular mortality.[1]

Among individuals who adhered to any type of vegetarian diet, the adjusted hazard ratio (HR) for all-cause mortality was 0.88 (95% CI 0.80-0.97), according to Michael J. Orlich, MD, and colleagues from Loma Linda University in California.

In survival analysis, the hazard ratio (HR) is the ratio of the hazard rates corresponding to the conditions described by two levels of an explanatory variable. For example, in a drug study, the treated population may die at twice the rate per unit time as the control population. The hazard ratio would be 2, indicating higher hazard of death from the treatment. Or in another study, men receiving the same treatment may suffer a certain complication ten times more frequently per unit time than women, giving a hazard ratio of 10.

And for men:

• Cardiovascular mortality was significantly lower:(HR 0.71, 95% CI 0.57-0.90)
• as was death from ischaemic heart disease (HR 0.71, 95% CI 0.51-1)

“Vegetarian dietary patterns have been associated with reductions in risk for several chronic diseases, such as hypertension, metabolic syndrome, diabetes mellitus, and ischaemic heart disease, which might be expected to result in lower mortality,”

However, previous mortality studies have had contradictory results, so Orlich and colleagues sought to clarify the uncertainty by analysing outcomes for 73,308 participants in the Adventist Health Study 2.

Mean age was 58, and roughly two-thirds were women.

Dietary patterns were assessed on a food frequency questionnaire at baseline.

Participants were classified as vegans if they avoided eggs, dairy, fish, and meat (7.6%); lacto-ovo-vegetarians if they ate eggs and dairy but avoided fish and meat (28.9%); pesco-vegetarians if they consumed fish but not meat (9.8%); and semi-vegetarian if they ate fish or meat no more than once weekly (5.5%).

The remaining 48.2% were nonvegetarians.

Adherence to the vegetarian diets ranged from 19 to 39 years.

During a mean follow-up of 5.79 years, there were 2,570 deaths.

While for men the risk all-cause mortality was significantly reduced (HR 0.82, 95% CI 0.72-0.94), the reduction for women was not significant (HR 0.93, 95% CI 0.82-1.05).

For men and women combined, no significant reductions in mortality from ischaemic heart disease, cardiovascular disease, or cancer were found, although there was a decrease for “other” causes of death (HR 0.85, 95% CI 0.73-0.99).

Unlike men, women had no significant reductions in deaths from cardiovascular disease or ischaemic heart disease.

Both male and female pesco-vegetarians had lower risk of all-cause mortality (HR 0.81, 95% CI 0.69-0.94), as did male and female lacto-ovo-vegetarians (HR 0.91, 95% CI 0.82-1).

Pesco-vegetarians also had reduced risk for death from ischemic heart disease (HR 0.65, 95% CI 0.43-0.97), and male pesco-vegetarian were at lower risk for death from cardiovascular disease (HR 0.66, 95% CI 0.44-0.98).

Men who followed a vegan diet fared particularly well:

• All-cause mortality, HR 0.72 (95% CI 0.56-0.92)
• Death from ischaemic heart disease, HR 0.45 (95% CI 0.21-0.94)
• Death from cardiovascular disease, HR 0.58 (95% CI 0.38-0.89)

“Vegetarian diets have been associated with more favourable levels of cardiovascular risk factors, and nutrient profiles of the vegetarian dietary patterns suggest possible reasons for reduced cardiovascular risk, such as lower saturated fat and higher fibre consumption,”

The researchers also looked at specific causes of mortality in the “other” category, and found that for both sexes, renal mortality was lower for all types of vegetarians (HR 0.48, 95% CI 0.28-0.82), as was mortality from endocrine causes (HR 0.61, 95% CI 0.40-0.92).

There were no clear reductions in deaths from cancer, the researchers pointed out.

“The heterogeneous nature of cancer may obscure specific diet-cancer associations in analyses of combined cancer mortality, and lack of significance may reflect insufficient power to detect weaker associations at early follow-up.”

It remains unclear why the effects were stronger in men.

“Future analysis will evaluate possible effect modification by sex for particular foods or nutrients, which may suggest sex-specific mechanisms,”

In an invited commentary, Robert B. Baron, MD, of the University of California San Francisco, noted that many people who choose to eat a vegetarian diet do so for ethical, religious, and environmental reasons, rather than for health benefits, and clinicians who advise patients on diet must keep those factors in mind.[2]

“First and foremost, dietary advice needs to be given to patients based on their own dietary history and preferences, their motivation to change their diet, and their clinical circumstances,”

Although nutrition authorities may disagree about the optimal balance of macronutrients in an ideal diet, and the amount of meat and other specific foods that should be ingested, virtually all agree that diets should limit added sugars and sugary drinks, refined grains, and large amounts of saturated and trans fats.

Limitations of the study included its short follow-up period and the potential for confounding by non-dietary factors.

References