>>>Preprint version of letter published in BMJ DOI:10.1136/bmj.c2765<<< Intelligence and the reduction of health inequalities Lager A, Bremberg S, Vågerö D In a recent editorial (1), Batty and colleagues discussed our work on intelligence and mortality (2) and came to the conclusion that “efforts to reduce inequalities should continue to be broadly based, including educational opportunities and interventions initiated in early life”. We fully agree with this conclusion. However, we wonder if this conclusion is consistent with the way they reason, in particular with their defence of four ideas about intelligence and health that we questioned in our paper, namely: (A) that intelligence is the fundamental cause of socioeconomic differences in health, (B) that the importance of intelligence for mortality is the same for men and women, (C) that early intelligence follows on from good health rather than the other way around, and finally (D) that intelligence might be a non-malleable trait, as efforts to improve it “so far [has] yielded disappointing results” (1).This last idea has often gone hand in hand with the idea that intelligence is, by and large, an inherited trait or, as it has been summed up, “substantially heritable” (3, 4). Do not these propositions suggest that the possibility of being able to reduce inequalities is fairly small? Luckily, there are empirical findings which paint a very different overall picture - one that is more promising when it comes to future public health measures. First, although propositions (A) and (C) above may have some truth to them, they do not seem to suffice as explanations. Given the magnitude of the associations between IQ and mortality (at least among men)(5), this should be enough for the intelligence-health literature to deserve attention from anyone interested in promoting health and/or health equity. Secondly, we believe (in contrast with proposition D) not only that intelligence can be promoted but that this is already happening, as demonstrated by the secular trend in intelligence, the so-called Flynn effect (6). The clear effect of schooling on IQ (7-9) has probably contributed to this trend (3, 10). The heritability of intelligence is actually not higher than that of several other phenomena relevant to public health. Childhood obesity, for example, has a genetic component that is as high as, or even higher than, the one for intelligence (11, 12). The prevalence of childhood obesity has tripled or so during the last 30 years in several countries (13). No one claims that this is for genetic reasons. Intelligence as well, certainly, is the result of interaction between genetics and the environment, including the social environment. Thus, it is only our own ignorance that stops us from formulating successful policies in this field. Batty et al also had a number of specific concerns about our paper. One was that using education as a primary marker of socioeconomic status is problematic because of collinearity, i.e. that education and intelligence are so highly correlated that education captures the effect of intelligence. In fact, the relatively high correlation was one reason why education was chosen as the marker of socioeconomic status, rather than occupation and income (see page 2 of our article), since this makes the testing of the hypotheses as sharp as possible. Given that we found associations with mortality for one factor net of the other, collinearity is something that would strengthen the conclusion that (for men) both are important, in themselves. A