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expert reaction to study looking at dairy consumption, cardiovascular disease and death

A study published in The Lancet that shows dairy consumption is associated with a lower risk of mortality and major cardiovascular disease events in a multinational cohort.

 

Prof Nita Forouhi, MRC Epidemiology Unit, University of Cambridge, said:

“There is a widespread misconception that eating dairy products is harmful for cardiovascular health, and this study lays that to rest once again, adding to other research.  So, dietary guidelines that promote consuming 2-4 portions of dairy a day are supported with new evidence in a worldwide context.  The key question of whether we should consume low-fat or full-fat dairy is not really fully answered by this research due to low intakes of low-fat dairy in much of the world except Europe and North America.  For now, current guidelines should be followed.  But this study certainly opens up debate and should serve as a stimulus for more research to tease out this issue on relative benefits of whole-fat versus low-fat dairy.

“This study’s result that dairy products are linked with cardiovascular health benefits is not new, but this study especially adds new knowledge in a global context across five continents as past research has almost exclusively been from developed Western nations.

“The PURE study uniquely included populations from 21 countries and showed that in this global sample, dairy consumption is especially beneficial in low-income and middle-income countries where traditionally dairy consumption is low.

“These are the first long-term data from many low-income and middle-income countries and should stimulate further research, including randomised clinical trials of dairy intake and intermediate endpoints such as weight, blood pressure, lipid/cholesterol levels and glucose control.

“The study has the ‘usual limitations’ of observational research, such as residual confounding (or alternative explanations) from factors that were not accounted for, and it also measured diet only once at baseline while diets may change over time, but there is a trade off between logistics, cost, and feasibility.  This is a starting point at the very least, with the need for further improved research in the future.”

 

Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“This is a large observational study conducted in countries that differ markedly with regard to income and genetics, which confound the conclusion.  The intake of milk products in those countries that consumed milk products was in the authors’ words “moderate”.  The participants were relatively young so the incidence of cardiovascular disease was low, so a much longer follow up is required before any firm conclusions can be drawn as noted in the accompanying editorial.

“High blood pressure is a major cause of stroke, which is more common in people of African and East Asian descent.  High blood pressure is more likely to be diagnosed and treated in high income countries.  The origin of hypertension may have its roots in early development in the womb and in early life, being more likely to occur when birthweight is low (more likely in poorer countries).  The study only looks at dietary data from a food frequency questionnaire completed in middle-aged adults and does not recognise that diets are changing rapidly with the globalisation of food.

“The authors suggest that countries where milk intake is low might benefit by consuming dairy products in terms of risk of cardiovascular disease.  But this fails to recognise that milk is poorly tolerated in many people of East Asian and African origin because of genetic difference in persistence lactase.  Many African and Asian adults get diarrhoea and severe bloating after drinking milk.  Furthermore, CVD rates are low in Japan a country where very few dairy products are consumed.

“In conclusion, this study has extrapolated its findings into dietary advice which does not seem justified given the limitations of the study.”

 

Dr James Doidge, Senior Research Associate, UCL Great Ormond Street Institute of Child Health, said:

“This study is not the first to suggest that moderate intake of whole-fat dairy is beneficial to health, but it is one of the largest.  All dietary research is made difficult by the long time period over which dietary risk accrues and ultimately leads to poor health.  This study followed a large number of participants for a 9 years, which is a relatively long time in this field of research.

“Dietary research is also often confounded by the relationships between diet, income and other lifestyle factors that affect health.  People with high incomes and healthier lifestyles often also consume more dairy products, which makes observational analyses such as this one tricky.  While the researchers have gone to great lengths to address this statistically, more interventional research (e.g. clinical trials) is desperately needed to confirm findings and explore the mechanisms through which they arise.

“This study also highlighted the unusual preference of the western world for reduced-fat dairy products, a preference that has been driven by dietary advice to reduce saturated or total fat consumption.  Guidelines about the selection of reduced-fat versus whole-fat dairy products are direly in need of updating; they are not based on the evidence about dairy products but rather on evidence about saturated fats that is itself being called into question in light of findings such as this study provides.  While the saturated versus unsaturated fat story was an enticing simplification, we are discovering that the truth is more complex.”

 

Victoria Taylor, Senior Dietician at the British Heart Foundation, said:

“Although the results sound quite striking this type of study only shows an association.  It can’t explain why the higher dairy intake was linked to lower risk of death and cardiovascular disease.  There are also a number of limitations to the research and so it’s important not to jump to conclusions about this study.  Dairy intake was only assessed at the start and so could have changed over the period of follow up.  There is also a question about how the dairy would be consumed in different countries and the overall quality of the diet and other lifestyle factors that could affect CVD risk of the participants.  The age range of the participants was also wide and those at the younger end would have been unlikely to die or have CVD, even within the 9 years of follow up which could have affected the results.

“Dairy products don’t need to be excluded from the diet to prevent heart and circulatory disease and are already part of the eatwell guide which is the basis for our healthy eating recommendations in the UK.  In this study the consumers with higher intakes were having about two to three portions of dairy a day, which is in line with current advice.

“Currently, it’s recommended that we choose reduced fat dairy as our overall intakes of saturated fat exceed recommendations, and this won’t change as a result of this research.  More and different types of research are needed to help us confirm the true role of dairy in relation to heart and circulatory disease.”

 

Prof Ian Givens, Institute for Food, Nutrition and Health, University of Reading, said:

“The PURE study is impressive and probably unique as it included data on the association between milk and dairy foods with mortality and cardiovascular diseases (CVD) from 21 countries in five continents with considerable variation in dairy consumption.  Commendably the work also tried to examine any differential effect of different dairy foods and high versus low fat products.  It is essential that we more fully understand these distinctions and whilst a good number of studies have looked at this there has been no general agreement on how to categorise the various foods.  The overall outcome that dairy consumption was associated with reduced risk of mortality and CVD events agrees with many earlier studies and meta-analyses but the fact that this study is large and geographically very diverse adds considerable weight to the overall picture.

“The findings also supports other evidence that there is not one simple relationship between consuming saturated fat and risk of CVD – the food vehicle delivering the fat can have a key influence.  The results of this study suggest that saturated fat from whole-fat milk, yoghurt and hard cheese has very limited if any impact on CVD risk.  The natural extension of this is the need for more food-based dietary recommendations.

“There are inevitably limitations to prospective studies and the authors comment on some of these.  An often criticised point is the use of dietary information collected only at baseline and then applied to long follow-up periods.  This was done in this study, and although the paper confirms that the association between milk intake at 3 years follow up and CVD was similar to that using baseline data, 3 years is still not long in a median follow up period of about 9 years when dairy consumption was probably increasing in some countries and reducing in others.  Nevertheless this is a valuable contribution to this important topic and highlights the need for detailed work to investigate the mechanisms involved.”

 

Dr Sarah Berry, Senior Lecturer in Nutritional Sciences, King’s College London, said:

“The evidence from the PURE study that the consumption of dairy foods is associated with lower risk of cardiovascular disease is consistent with previously published epidemiological studies and is supported by randomised controlled trials.

“Dairy products consist of a diverse group of foods of varying nutrient composition with a complex food matrix and therefore it is important to consider the health effects of the main categories of dairy foods separately, as was done in the PURE study.  The findings from PURE support the current evidence that yoghurt (a fermented dairy product) and milk has a beneficial effect, whilst butter (non-fermented dairy) showed a non-significant trend for a negative impact on mortality and cardiovascular outcomes.  However, it is surprising that cheese (a fermented dairy product) was not associated with a significant positive effect on total mortality or cardiovascular disease as previous epidemiological studies and randomised controlled trials have reported that cheese consumption lowers the risk of CVD.

“Beyond the limitations in the PURE study which have already been heavily reported when the first paper was published in 2013 (including use of food frequency questionnaires, lack of differentiation between refined and complex carbohydrate, lack of dietary intake follow up and more), a key limitation in this new analysis from the PURE study is the lack of inclusion of butter and cream in the total dairy and the whole-fat dairy groups.  Due to the reported trend for increased risk of total and cardiovascular mortality with increasing levels of butter intake in PURE, the inclusion of butter into the ‘Total dairy’ and ‘Whole-fat dairy’ groups may have reduced the strength of association between diary intake and positive health effects.

“It is important to note that similar beneficial effects were observed in PURE for whole fat dairy and low-fat dairy consumption on mortality and cardiovascular disease.  Therefore, whilst this evidence shows that there is no added benefit in terms of cardiovascular risk of opting for low fat over high fat milk, yoghurt or cheese dairy, for those wanting to reduce their calorie intake, low-fat dairy may be a preferred option.

“The perceived negative effects of dairy products have been in part due to the traditional reductionist and single nutrient, single biomarker approach to making associations between foods and health.  For example, because dairy foods are high in saturated fat they were considered unhealthy.  However dairy foods are nutrient dense and contain essential vitamins, minerals, macro- and micro- nutrients within a complex food matrix with probiotic functions.  Further, as we consume foods and not nutrients, the results from the PURE study highlight the importance of food-based guidelines, and not nutrient based guidelines, in the context of healthy dietary patterns.”

 

Declared interests

Prof Nita Forouhi: “None.”

Prof Tom Sanders: “Honorary Nutritional Director of HEART UK.  Scientific Governor of the British Nutrition Foundation.  He is now emeritus but when he was doing research at King’s College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks.  In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011.  This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof Hough at the Queen Elizabeth College (QEC), which merged with King’s College London.  The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar.  Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006.  Tom also used to work for Ajinomoto on aspartame about 8 years ago.  Tom was a member of the FAO/WHO Joint Expert Committee that recommended that trans fatty acids be removed from the human food chain.  Tom has previously acted as a member of the Global Dairy Platform Scientific Advisory Panel and Tom is a member of the Programme Advisory Committee of the Malaysian Palm Oil Board.  In the past Tom has acted as a consultant to Archer Daniel Midland Company and received honoraria for meetings sponsored by Unilever PLC.  Tom’s research on fats was funded by Public Health England/Food Standards Agency.”

Dr James Doidge: “I have previously conducted research that was supported by funding from Dairy Australia.  I currently have no ties to the dairy industry.”

Victoria Taylor: “No interests to declare.”

Prof Ian Givens: “I have received small amounts of funding for speaking engagements from The Dairy Council and The European Dairy Federation with contributions to research from The Global Dairy Platform and in kind contributions from a major dairy company.  In no case did any of these organisations influence what I said or the design of studies.”

Dr Sarah Berry: “I currently receive funding from: Malaysian Health Ministry; BBSRC; Zoe Global; Almond Board of California.”

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