Participants of the 1970 British cohort study with higher intelligence test scores in childhood were more likely to report being a vegetarian at age 30 years. This relation was partly accounted for by educational attainment and by occupational social class in adult life but remained statistically significant after adjustment for these factors.
Several investigators have examined the link between education (a strong correlate of mental ability15
) and vegetarianism. Findings are mixed. Pooled data from a meta-analysis of vegetarianism and mortality11
showed that of four studies reporting data on educational attainment two showed higher levels in vegetarians than in non-vegetarians, whereas in two other studies the opposite association was seen. In previous analyses of the 1970 British cohort study, a greater consumption of non-meat products, such as bread or fresh fruit, was apparent in people with high educational attainment.16
Although the vegetarians in this cohort were, on average, more intelligent, better educated, and of higher occupational social class than the non-vegetarians, these socioeconomic advantages were not reflected in their income. It may be that ethical considerations determined not just their diet but also their choice of employment. Compared with non-vegetarians, vegetarians were less likely to be working in the private sector and more likely to be working in charitable organisations, local government, or education: 17% of the vegetarians worked in education compared with 9% of non-vegetarians. When asked, as part of the follow-up survey, what they thought of the statement “The government should redistribute income,” 50% of vegetarians said they agreed compared with 41% of non-vegetarians, and this proportion was even higher among male vegetarians (61% v 42%). Such views may not be compatible with a career in the more lucrative employment sectors.
Some of the participants who reported being vegetarian said they consumed fish or chicken. We found no difference in IQ scores, or any marker of socioeconomic status, between this group and the strict vegetarians. It may be that vegetarianism exists as a continuum, with those who describe themselves as vegetarian but who are prepared to eat white meat or fish (flesh that is paler and less obviously meaty than beef, pork, or lamb) having the same trait but less of it than those who avoid consuming any animal flesh.
The strengths of this study are its size, resulting in high statistical power; the representativeness of the sample, resulting in a high degree of generalisability for the British population born around the same time; and the breadth of data on socioeconomic status, allowing an examination of the role of potential confounding and mediating variables.
Our study also has some limitations. Firstly, some attrition has occurred in the cohort over time. The participants at the 30 year follow-up did gain significantly higher IQ scores at age 10 than those who did not take part, although the size of the differences was modest (0.3 of a standard deviation). Unless the relation between childhood mental ability and vegetarianism is in the opposite direction in non-participants, little bias will have been introduced in our study. Secondly, we had no information from the 30 year follow-up on how long our participants had been vegetarian. Evidence from a subset of 3795 participants (46.5%) who had taken part in a previous follow-up of the cohort when they were aged 16 years suggests that most of those who were vegetarian at age 30 had chosen that type of diet as adolescents or young adults, some years after their IQ was measured: among these 3795 participants, only 32% of those who were vegetarian at age 30 were already vegetarian at age 16, and of those already vegetarian at age 16 95% had become vegetarian between the ages of 11 and 16. The difference in childhood IQ scores between vegetarian and non-vegetarian participants at age 30 was also apparent at age 16; compared with non-vegetarians at this age, those who were vegetarian scored on average 4.1 points higher on the mental ability test at age 10.
Although our results suggest that children who are more intelligent may be more likely to become vegetarian as adolescents or as young adults, it does not rule out the possibility that such a diet might have some beneficial effect on subsequent cognitive performance. Might the nature of the vegetarians' diet in this cohort have enhanced their apparently superior brain power? Was this the mechanism that helped them to achieve the disproportionate number of higher degrees? Benjamin Franklin and George Bernard Shaw, both ardent vegetarians, would have us believe so. According to Shaw in an article published in The Star in 1890, “A mind of the calibre of mine cannot derive its nutriment from cows.” Even Shakespeare, not known for his vegetarian sensibilities, expressed through Sir Andrew Aguecheek in Twelfth Night (Act 1, Scene 3) a belief in the deleterious effects of consuming meat; “I am a great eater of beef and I believe that does harm to my wit.” Further research may be needed to explore this hypothesis.
Our finding that children with greater intelligence are more likely to report being vegetarian as adults, coupled with the evidence on the potential benefits to cardiovascular health of a vegetarian diet, may help to explain why higher IQ in childhood or adolescence is linked with a reduced risk of coronary heart disease in adult life. Additional studies of older cohorts with data on cardiovascular risk factors will be needed to examine the extent to which vegetarianism mediates the association between childhood IQ and coronary heart disease.
Alternatively it is possible that the link between childhood IQ and vegetarianism in later life is not on a causal chain of mechanisms related to health. People with a higher IQ may well differ from those with less superior brain power in many of their lifestyle decisions: for instance, choice of newspaper, type of books read, preferred form of entertainment. The association between IQ and vegetarianism may be merely an example of many other lifestyle preferences that might be expected to vary with intelligence but which may or may not have implications for health.
What is already known on this topic
Vegetarianism may be viewed by those of higher intelligence as a healthier option than consuming meat
What this study adds
Higher scores for IQ in childhood are associated with an increased likelihood of vegetarianism in adulthood