Tag Archives: Salt

An Issue of BMJ with Multiple Studies on Diet

This News Blog often contains information about diet and health. For example, we have cited evidence that salt is enemy number one [1]; trans-fats are unremittingly bad news [2]; and large amounts of sugar are harmful.[3] After that the risks become really rather small – relative risks of about 20%. Fruit, and more especially vegetables, are good news. Milk is an unhealthy drink in adults (never intended for that purpose and galactose is harmful, unless removed during a fermentation process).[4] Three further studies of diet were included in a single recent issue of the BMJ.[5-7]

The first study by Etemadi, et al. looked at meat consumption in a large cohort of people (n= 536,969) who gave detailed dietary histories.[5] The evidence corroborates other studies in showing that red meat is harmful, increasing relative risk of death by about 20% in high meat eaters compared to moderate meat eaters. The difference is greater if the comparison is made with people who obtain almost all of their meat in the form of fish and chicken. The causes of death that showed greatest increases in risk with high red meat consumption were cancer, respiratory disease and liver disease. Surprisingly, perhaps, increased risk from stroke was nugatory. The increased risk in unprocessed meat is probably related to haem iron, and in processed meat to nitrates/nitrites – there are all pro-oxidant chemicals. Of course this is an association study, so some uncertainty remains. The main problem with meat, as the BMJ Editor points out,[8] is the harmful environmental effects; apparently animal husbandry contributes more to global warming than burning fossil fuels. I take the environmental effects seriously – perhaps we will one day vilify meat farmers more vociferously than we currently vilify tobacco farmers. After all, individuals don’t have to smoke, but cannot protect themselves from the harmful effects of pollution.

Meanwhile, for those who are interested, the other two relevant articles in this issue of the BMJ looked at avoiding gluten in people who do not have celiac disease (no benefit and evidence points towards harm),[6] and the beneficial effect of a low salt and fat diet on gout.[7]

— Richard Lilford, CLAHRC WM Director

References:

  1. Lilford RJ. Effects of Salt in Diet. NIHR CLAHRC West Midlands News Blog. 17 October 2014.
  2. Lilford RJ. On Diet Again. NIHR CLAHRC West Midlands News Blog. 23 October 2015.
  3. Lilford RJ. How Much Sugar is Too Much? NIHR CLAHRC West Midlands News Blog. 25 September 2015.
  4. Lilford RJ. Two Provocative Papers on Diet and Health. NIHR CLAHRC West Midlands News Blog. 12 December 2014.
  5. Etemadi A, Sinha R, Ward MH, Graubard BI, Inoue-Choi M, Dawsey SM, Abnet CC. Mortality from different causes associated with meat, heme iron, nitrates, and nitrites in the NIH-AARP Diet and Health Study: population based cohort study. BMJ. 2017; 357: j1957.
  6. Lebwohl B, Cao Y, Zong G, Hu FB, Green PHR, Neugut AI, Rimm EB, Sampson L, Dougherty LW, Giovannucci E, Willett WC, Sun Q, Chan AT. Long term gluten consumption in adults without celiac disease and risk of coronary heart disease: prospective cohort study. BMJ. 2017; 357: j1892.
  7. Rai SK, Fung TT. Lu N, Keller SF, Curhan GC, Choi HK. The Dietary Approaches to Stop Hypertension (DASH) diet, Western diet and risk of gout in men: prospective cohort study. BMJ. 2017; 357: j1794.
  8. Godlee F. Red meat: another inconvenient truth. BMJ. 2017; 357: j2278.

Recent History of Anti-Hypertensive Treatment Trials

An interesting essay by Pfeffer and McMurrary traces the recent history of trials of anti-hypertensive therapy.[1] The authors chronicle the scientific evidence that has accumulated to show that treating hypertension lowers the risk of stroke, heart disease and death; that systolic blood pressure is very important; that outcomes are improved, even if the starting blood pressure is only slightly raised (particularly in diabetes); but that it is also possible to try too hard to control blood pressure. No mention here of salt, which is important in the genesis and maintenance of hypertension. However, this is a readable account of how the scientific and ‘social’ discovery of how to treat the ‘silent killer’ that is hypertension progressed hand in hand.

— Richard Lilford, CLAHRC WM Director

Reference:

  1. Pfeffer MA, & McMurrary JJV. Lessons in Uncertainty and Humility – Clinical Trials Involving Hypertension. New Engl J Med. 2016; 375: 1756-66.

Reversible Environmental Factors and the Global Burden of Disease

The Global Burden of Disease study is an extraordinary collaborative effort to document the health of the human race. It produces a series of weighty publications every four years, packed with interesting detail. The most recent set of papers have been published and the first deals with life years lost.[1] The study documents the recent epidemiological transition in which non-infectious diseases have taken over from infectious diseases as the main cause of life-years lost across the world. Childhood malnutrition is no longer enemy number one, relegated to fourth place globally, but it retains the number one slot in sub-Saharan Africa. High blood pressure, smoking and obesity now occupy the first three slots globally. CLAHRC Africa includes a programme of research on salt. Salt is now enemy number two, after smoking, in unhealthy behaviours. Research into methods to reduce salt intake is a priority, even as the debate continues into whether sodium levels can fall too low – some data suggest a J-shaped distribution of risk with rising salt intake. Unsafe sex is the major risk factor in East, and Southern Africa, while South Africa is the country with the world’s highest burden of disease associated with reversible environmental factors. Areca nut (another interest of CLAHRC Africa) does not make it onto the list. Along with smokeless tobacco, the CLAHRC WM Director thinks this risk should be considered for inclusion in further versions. Another criticism is double counting – high sodium intake and high systolic blood pressure both appear on the list, yet the former is a prominent cause of the latter. To be fair, the authors do recognise this issue. In a future blog we will report on a further analysis of the remarkable GBD dataset to consider not just the deaths, but the total burden of disease (for instance in Disability Adjusted Life Years [DALYs]).

— Richard Lilford, CLAHRC WM Director

References:

  1. GBD 2013 Risk Factor Collaborators. Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks in 188 countries, 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet. 2015; 386: 2287-323.

Use of Language: Race is to Ethnicity as Sex is to Gender

The CLAHRC WM Director has often puzzled over the use of “gender” vs. “sex”, and “ethnic group” vs. “race” in scientific writing. They are not synonyms; gender and ethnicity are social constructs, while and sex and race are biological. The former are not “polite” terms for the latter. Philip Steer, Emeritus Editor of an exceptionally lively speciality journal BJOG: An International Journal of Obstetrics and Gynaecology, has written a sure-footed article on this topic.[1] Agreeing that race is the appropriate term to describe groups with a similar place of origin, irrespective of culture, he recommends the National Library of Medicine MeSH groupings. Five continental groupings (African, American, Asian, European, and Oceanic) are broken down by sub-region – for example, European into ‘White European’ and ‘Mediterranean’. Gone is the term Caucasian, which was used to describe broader origins than just the Caucasus area and which, the CLAHRC WM Director learned, has eugenic overtones.

The article makes some other interesting points. Africa has the greatest human genetic diversity among the continents, accounting for as much as 80% of all human genetic variation. This is because of the bottleneck created by the exodus from Africa of a relatively small group of Homo sapiens about 70,000 years ago. These migrants mated with Neanderthals and spread out to colonise the rest of the globe. All of this is of interest to CLAHRC Africa, which has an interest in preventing hypertension and stroke. Salt is the prime causal suspect and there is evidence that some African people may be especially prone to salt-induced hypertension as a result of a widespread allele. Since intake of salt has increased rapidly over the past century we are developing protocols to identify the main source of salt in the diet. In due course we will design an intervention to tackle this. We are working closely with colleagues in the African Population Health Research Center (APHRC) and Malawi on this project.

However, the whole question of race will become progressively less important in science and medicine in the future for two reasons. First, gene sequencing will increasingly enable scientists and doctors to hypothecate genetic variation at the individual level, rather than the level of the group/race.[2] [3] The arrival of personalised medicine will reduce the importance of race and it has always been the case that there is far more variation within, than between races. Second, mating across racial boundaries will increasingly dilute correlation between race and genetic configuration and vitiate the effects of Homo sapiens great migration out of Africa.

— Richard Lilford, CLAHRC WM Director

Reference:

  1. Steer P. Race and Ethnicity in Biomedical Publications. BJOG. 2015: 122(4): 464-7.
  2. Burchard EG, Ziv E, Coyle N, et al. The Importance of Race and Ethnic Background in Biomedical Research and Clinical Practice. New Engl J Med. 2003; 348: 1170-5.
  3. Jeffers C. The Cultural Theory of Race: Yet Another Look at Du Bois’s “The Conservation of Races”. Ethics. 2013; 123(3): 403-26.

Effects of Salt in Diet

Well there you have it, salt really is bad for you – based on a study of 107 randomised comparisons on the effects of reduced sodium intake on blood pressure, 99 cohorts on the effects of blood pressure on cardiovascular mortality, and a survey of the salt intake of three-quarters of all adults in the world.[1] It is hard to argue with the results of a study like that. Modelling based on the data from the above study, funded by the Bill and Melinda Gates Foundation, concludes that one in every ten deaths from cardiovascular disease can be attributed to a high salt intake. Incidentally, having 107 randomised comparisons makes it possible to examine the correlation between the reduction of salt intake in those trials, and the reduction in blood pressure. It turns out to be linear.

— Richard Lilford, CLAHRC WM Director

Reference:

  1. Mozaffarian D, Fahimi S, Singh GM, Micha E, Khatibzadeh S, Engell RE, Lim S, Danaei G, Ezzati M, Powles J. Global Sodium Consumption and Death from Cardiovascular Causes. NEJM. 2014; 371: 624-34.