The chemist Sir Humphrey Davy (1778–1829) said: ‘Nothing is so fatal to the progress of the human mind as to suppose that our views of science are ultimate … that our triumphs are complete … that there are no new worlds to conquer’ (Riegels and Richards, 2011). This invites the heart-warming inference that scientific progress is not so much dependent on consensus as on debate, argument – which can generate both heat and light – and even controversy.
One area of current controversy is the nature of the relationship between salt, blood pressure and cardiovascular disease, and I found it puzzling to read an editorial, whose author, in addressing the issue of population strategies for salt consumption, stated: ‘When apparent dogma is challenged, we should speak not of controversy but rather accede to the all-encompassing expression of so-called scientific uncertainty, so as to avoid unbecoming rhetoric’ (O'Brien, 2016).
But perhaps it is one's duty to the scientific process to challenge and expose dogma, even if it causes controversy, rather than ‘accede to the all-encompassing expression of so-called scientific uncertainty’. For instance, the sports drinks industry and its apologists have long favoured the dogma that extra sodium should be consumed during endurance exercise. Thus, Armstrong et al (1993) wrote that ‘electrolytes (primarily NaCl) should be added to the fluid replacement solution to enhance palatability and reduce the probability for development of hyponatremia’. But sports scientist Prof Tim Noakes, whose team had discovered in 1985 why the potentially fatal exercise associated hyponatraemia (EAH) occurs, brushed any ‘scientific uncertainty’ or ‘unbecoming rhetoric’ aside with a blunt: ‘There is no published evidence showing that the ingestion of sports drinks containing sodium chloride at concentrations that are palatable can prevent the development of EAH … in those who overdrink …’ (Noakes, 2012).
Nuance is one thing; but to cloak published work that is wrong with the mantle of ‘scientific uncertainty’, when unequivocal condemnation is needed, confers too much politesse upon those who may not deserve it. The definition of rhetoric which I favour – O'Brien (2016) doesn't offer one – is the art of using language to persuade or influence others. On occasion it is appropriate to deploy rhetoric, unbecoming or not.
Meanwhile, salt-related controversies continue, and in their review of the history of the topic, DiNicolantonio and O'Keefe (2017) note that early studies that reported benefits of salt restriction among those with hypertension were based on uncontrolled case reports; results from well-designed, controlled studies indicated that the results of low-salt diets were effective in only around 25% of those with hypertension; overall evidence in the first half of the 1900s suggested that low-salt diets were unreasonable strategies for treating hypertension; and during that same period, low-salt diets were considered unpalatable by many clinicians, who judged them to lead to serious adverse consequences.
But only recently, He et al (2021) make clear that ‘[t]here is a causal relationship between dietary salt intake and blood pressure. A reduction in salt intake from the current world average of 10 g/day to the [World Health Organization] WHO recommended level of less than 5 g/day, lowers blood pressure and lowers the risk of cardiovascular disease and all-cause mortality’. However, three of the four authors are members of the salt-reduction organisation World Action on Salt and Health. Yet in the same journal the title of a paper by O'Donnell et al (2020) sums up an opposing view: ‘Salt and cardiovascular disease: insufficient evidence to recommend low sodium intake’. And in a tightly argued counterblast to the argument that a low salt intake helps to confer protection against cardiovascular disease, DiNicolantonio (2017) not only asserts that most of us need not guard against excessive salt consumption, but presents peer-reviewed evidence that salt can exert a protective effect against insulin resistance, diabetes, and heart disease.
Where do we go from here? It is a question that is asked by Alderman (1997), who makes the reasonable observation that ‘[c]alls for consensus are not likely to quell the noisy dispute about salt. A healthy scientific environment can often generate disquieting controversy. Happily, however, the result may be important new knowledge. It may even be that one dietary size will not fit all’.
It is an approach that Sir Humphrey Davy would have approved of.