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Thursday, April 24, 2014

US Salt intake ~ No change in 40 years

In 1977, The US Senate Select Committee on Nutrition and Human Needs issued the 1st edition of Dietary Goals for the United States. One of the recommendations was to: “Reduce salt consumption by about 50 to 85 percent to approximately 3 grams per day”. This equated to 1,200 milligrams of sodium, which is the element of salt (sodium chloride) implicated as a contributory factor for the development of hypertension. This is slightly below the current sodium recommendations of the American Heart Association of <1,500 milligrams per day but is half what the Institute of Medicine set out as a target for the US population in its most recent report on dietary guidelines (2,300 milligrams per day). Whatever the figure, which the public is blissfully ignorant of, a campaign to lower salt intake has been in operation now for almost 50 years. Two recent papers have looked at the pattern of salt intake in the US over that period.

Measuring salt intake in our diet is very difficult because, over the short periods that dietary surveys are completed (1-4 days) salt intake can fluctuate dramatically. An equally important limitation in this area is the accuracy of food composition tables as to salt levels in foods. It should be noted that over 80% of salt intake comes from foods and not the saltcellar. Thus an alternative to measuring salt intake is to measure salt excretion, specifically sodium excretion, since the body does not normally accumulate sodium and thus the quantity excreted over 24 hours should roughly equal the amount ingested over the same period.

Collecting all ones urine over a 24-hour period is very difficult. The subjects have to carry a 5 liter plastic container with them throughout the day and everywhere they go and they have to bring the container to the bathroom to collect all of the urine excreted at each urinary event. Thus, not surprisingly, such studies tend to have relatively small numbers. Researchers at the Harvard School of Public Health searched the literature for all studies that involved a 24-hour urinary sodium excretion measure among US citizens over the period 1957 to 2003[1]. They found 38 studies. Of these, 5 were large with an average of 2,900 subjects but the remaining 33 were relatively small with an average of <400 subjects per study. The average daily output of sodium in milligrams per 24 hours was 3,526 prior to 1980, 3,418 across the ‘80s, 3,499 across the ‘90s and 3,849 post-2000. Thus over the 40 years from the 1970’s, there was no significant change in daily sodium excretion and the estimated average daily intake of sodium was 3,526 milligrams per day, well above any of the dietary guidelines issued.

Recently, another study on trends in sodium excretion was published in which a single urine sample (“spot” urine sample) was used to extrapolate to a 24-hour sodium excretion using adjustment equations set about by an international research consortium called INTERSALT. In this study, they used random samples from the US National Dietary Surveys[2].  Overall, they also found no change in sodium excretion over the period 1988 to 2010 (3,160 mg/d for 1988-1994, 3,290mg/d for 2003-2006 and 3,290 for 2010). This equated to a daily sodium intake of 3,317 milligrams per day, which is very close to what the Harvard researchers found.

What do we take from these findings of a complete resistance to change in sodium intakes? Reducing sodium in the human food chain is quite different to reducing the levels of fat or sugar (the other two so-called  “evils” of modern food). There are techniques and technological solutions, which allow sugar intake to be reduced without a loss of sweetness and also for fat reduction without the loss of the mouth feel of fat. That is not the case for salt. If the level of salt intake is reduced in breads it needs to be done over a long period so that consumers slowly adapt their palate to lower salt levels.  There is no adequate sodium alternative.

There is a second way to look at these data. According to the Darth Vaders of public health nutrition who would protect us all from the inferior aspects of the  modern diet, the food industry has dramatically manipulated salt, fat and sugar levels in foods over the last 40 years to manipulate our palate and their sales. As Michael Pollan put it in his book “In Defense of Food”:
“Today foods are processed in ways specifically designed to sell us more food by pushing our evolutionary buttons-our inborn preferences for sweetness and fat and salt”.

If salt intake hasn’t changed between the early 70’s and today, a 40-year period, then, has the food industry failed in their attempts to push our evolutionary button for salt preference? To me, the most likely explanation is very simple. Those who promulgate a food conspiracy, do so without addressing the available evidence on food and nutrient intake patterns, which should guide their thinking. But regrettably, when individuals set our their stance on some issue of science, it is rarely for changing, whatever the data might say.

[1] Bernstein AM & Willett WC (2010) AJCN 92, 1172
[2] Pfeiffer CM et al (2014) J Nutr 144, 698

Monday, March 31, 2014

Organic food does not protect against cancer

The Soil Association[1] was founded in 1946 and today is the main body for the certification of organic farms in the UK. It’s website has a section on pesticides, which states the following: “Around 31,000 tonnes of chemicals are used in farming in the UK each year to kill weeds, insects and other pests that attack crops. There is surprisingly little control over how these chemicals are used in the non-organic sector and in what quantities or combinations. What we do know is that 150 of the available 311 pesticides commonly used have been identified as potentially causing cancer and many of us would have been exposed to these pesticides before we were born”. It then goes on to state: ”Even food that we think is healthy, such as non-organic Cox's apples, can be sprayed 18 times. The most dangerous chemicals used in farming, such as organophosphates, have been linked with a range of problems including cancer, decreasing male fertility, foetal abnormalities, chronic fatigue syndrome in children and Parkinson's disease”. This linking of organic food with a reduced exposure to so-called cancer-causing pesticides is a widely held belief among organic food advocates.
That view within the organic movement is unlikely to be changed by a recent study refuting this belief but the majority of people who are made to worry about this alleged pesticide-cancer link will take solace from its findings. The paper, published in the British Journal of Cancer[2] was based on data from The Million Women study, which was based on a million women screened for breast cancer, followed these women over a 12 year period with questionnaires on lifestyle completed at baseline and at years 3, 8 and 12. In the year 3 questionnaire, women were asked about their consumption of organic food within categories, “never”, “sometimes”, “usually” or “always”. A total of 751,975 provided data on their organic food intake in year 3. In this particular study part of the study, women were excluded if they had changed their diet in the previous 5 years because of an illness. That then left the researchers with data on 623,080 women.

At the outset of the study, 30% of women reported never consuming organic food, 63% sometimes consumed organic food and 7% reported always or usually eating organic food. During the follow up period of almost 9 years, a total of 53,769 women were diagnosed with some form of cancer. The authors looked at the relative risk of 16 cancers across the frequency of use of organic food. They controlled for age, area of residence, body mass index, smoking, physical activity, alcohol intake, age at first birth, fibre intake and type of meat intake. Compared to women who never consumed organic food, there was a 9% greater incidence of cancer among women who usually or always consumed organic food. The one exception was Non-Hodgkin Lymphoma (NHL) where those who usually or always consumed organic food had a 21% lower risk of NHL than women who never consumed organic food.

Already the organic movement is claiming that the 21% reduction in NHL is proof that pesticides are a causative factor in cancer. However, NHL in the UK accounts for just 4% of all cancers. Thus there were 161,215 cases of cancer among UK women in 2011 of which 155,358 or 96% of all cases did not involve NHL with cancer of the breast, bowel, lung, uterus and ovaries accounting for 62% of all cancers[3]. No matter what way the organic advocates dredge the data, the simple fact remains that the consumption of organic food had no overall protective effect against cancer (indeed it was 9% higher in the organic food consumers).
Plants maintain a natural defence system against pests and thus the overall load of exposure to natural pesticide is enormous concerned to our exposure to pesticides used in agriculture whether for commercial or organic agriculture. Data shows that using the rodent carcinogenic model, of the plants natural pesticides, 55% were positive carcinogens and 45% were not[4]. All available data show that about half of all naturally derived chemicals are positive in the rat carcinogenic model. The figure for all synthetic chemicals is also about 50%. Natural doesn’t equate with safety. Think of hemlock, magic mushrooms, opium, caffeine and nicotine to name a few.

People make all sorts of decisions about their lifestyle including diet. Some opt to be vegetarian. Some prefer to eat organic food. Some choose food based on a perceived allergy. The reasons are endless. So live and let live but please don’t preach about the health virtues of organic food to consumers who are not so inclined for whatever reason. Enjoy your food whatever your choice and let others enjoy theirs. There are many great challenges facing us in terms of public health nutrition. This paper, the first of its kind, has binned the claim of the organic food movement that consuming conventionally farmed foods can lead to exposure to cancer causing pesticides.

[2] Bradbury KE et al 2014 March 24 (e print ahead of publication)
[4] Ames BN & Gold LS (1997) FASEB J. 1Nov;11(13):1041-52

Friday, March 7, 2014

Food outlets, schools and obesity related outcomes

Understandably, there is a very strong focus in obesity research on the diets of schoolchildren with many schools now attempting to implement healthy eating policies.  Equally, there has been considerable concern about the existence of food retail outlets nearby to schools to which the schoolchildren have access. A group at the University of Oxford has recently published a meta-analysis of all relevant studies, which set out to examine the relationship between obesity outcomes and the proximity of food retail outlets to schools[1].

The authors completed a search of 10 on-line library databases and identified several thousand studies but, as ever, in meta-analyses, many of the initial studies were rejected for a variety of reasons leaving the authors with 30 full studies which met all of the a priori inclusion criteria. Each study had to have defined exactly what was meant by the retail food environment and to have measure quantitatively the relationship between food purchase patterns and obesity-related outcomes. Most of the papers were published between 2011 and 2013 and most were cross-sectional with children ranging in age from five to seventeen years. More than three quarters had sample sizes of over 1,000.

Of the 30 studies, the majority used a defined “buffer zone” around the school but some used route maps between the pupil’s home and school. GIS (Geographic Information Systems) software was the main source of information on retail outlets either within the designated buffer zone or school route. In general the buffer zone applied a distance of between 0.1 to 3.0 miles while the route approach generally used distances of 50 to 100 meters from the road travelled to and from school. The main outcome studied was the child’s BMI (kg/m2). The second most frequent measure of outcome was food intake but this appeared generally to be related to a narrow range of foods: fruit and vegetables, soda drinks or fast food. Some of course used several measures and just three used the overall diet quality index of the schoolchildren which would have included all sources of foods at all times of the day.

One study focused on fast food purchases and found a statistically significant positive association between fast food purchasing and the density of fast food outlets.  Ten studies examined the relationship between food outlets in general  and the consumption of sugar sweetened beverages and of fast food, including crisps, sweets, biscuits, fried food, sugar sweetened beverages and fast foods. Within these 10 papers, a total of 54 associations were examined and only two of these showed a statistically significant association. Four papers examined the association between fruit and vegetable consumption and food retail outlets and within these a total of 32 associations were examined. Only three showed statistically significant associations. Within the 30 studies, only three had data on the overall quality of the pupil’s diet and food retail outlet density. Two of these showed a significant association between diet quality of food outlets. In one case, the data showed a significantly higher diet quality index among pupils attending a school where the nearest retail outlet was greater than 1 km away as compared to those where the distance was less than 1km away. The second study found that the greater the distance to the nearest grocers the better was the overall diet of the pupils.

This is an important paper for several reasons. Firstly, it is a very well conducted study published in a high impact journal. Secondly, it highlights how the existence of evidence is happily ignored by those policy makers who want to place restrictions on the availability of food outlets within the vicinity of schools. Thirdly, it shows that the outcome variables which are easy to measure such as fruit and vegetable intake, soda intake or BMI yield fairly useless conclusions since they do not relate the one aspect of the determinants of food choice (school associated food outlets) to the totality of the effects of all food choice in terms of overall daily nutritional quality. Once again, we see a majority of studies in what is a very important area of public health nutrition, bedevilled by bad design. In the three studies, which did look at the overall quality of the pupil’s diet and density of food retail outlets two showed some significant associations. Now do two swallows make a summer?. No, but they point the way forward for the conduct of scientifically rigorous studies in this very important area of public health nutrition. To discover that the proximity of food outlets influenced specific food intake is of zero importance in public health nutrition. We need to know the full accurate daily nutrient intakes and only then can we judge whether any aspect of the obesigenic environment id truly influencing overall nutritional quality.

[1] [1] Williams J et al (2014) Obesity reviews Jan 13th (e pub ahead of print)

Sunday, February 16, 2014

Women's health: Cancer, Heart Disease and Misfearing

This blog is based largely on a recent paper in the Perspective series of the prestigious New England Journal of Medicine by US cardiologist Lisa Rosenbaum, entitled:” ‘Misfearing’ – Culture, Identity and Our Perceptions of Health Risks”[1]. First let me explain the term “misfearing”.  It is characterised by two attributes. It describes the widespread human tendency to base fear on emotive reasons and not on fact. It is also characterised by fear of dreadful events, which catch headlines and which are quite often rare (plane crashes, nuclear accidents, severe weather, HIV-AIDS etc.) rather than by fear of the familiar such as heart disease, obesity, smoking which are common and which occupy a great % of the health budget. Rosenbaum discusses this concept of misfear in relation to women’s health and specifically female cancer and female heart disease.

The majority of women would say that breast cancer is a bigger threat to women’s health than heart disease. However, the facts are the reverse, hence the concept of misfearing. In the US, over the period 2006 to 2010, the number of cases of all cancers in women was 2.8 million. The comparable figure for heart disease was 12.7 million, 4.5 times greater. The data skeptics will immediately argue that the heart disease data are flooded by statistics on high blood pressure, high blood cholesterol as well as actual cases of heart attack.  So let us consider deaths from cancer and heart disease in women. During this same period, 40,000 US women died from all forms of cancer. The comparable figure for deaths from heart disease was 410,000. Now, as regards mortality, the difference between all causes of female cancer and female heart disease is 10 fold.  Ten times as many graves of women who died of heart disease compared to all forms of cancer combined.

Why therefore is female health to a considerable health dominated by cancer, specifically breast cancer? The answer is largely sociological. But first consider the power and emotion behind the misfear of breast cancer. Rosenbaum points out that in 2009, the US Preventative Services Task Force recommended that the frequency of mammography in younger women should be reduced noting “…the potential harms outweighed the benefits”. The reaction among women was powerful. USA today conducted a poll of women aged 35 to 49 years and 84% intended to ignore the recommendations. So powerful was the backlash that the Affordable Care Act ignored the task force’s recommendations requiring insurers to base coverage on previous screenings. This perpetuated in law, a policy that the experts deemed did more harm than good. Rosenbaum writes: “Have pink ribbons and Races for the Cure so permeated our culture that the resulting female solidarity lends mammography a scared status? Is it the issue that breast cancer attacks a part of the body that is so fundamental to female identity that, to be a woman, one must join the war on this disease?”

I Googled the term “Famous women who have had breast cancer” and from the 20 listed, here are the ones whose names I recognise: Singers Kylie Minogue, Olivia Newton John, Sheryl Crow, and Carly Simon, actresses Cynthia Dixon of Sex and the City, Dame Maggie Smith, and Angelina Jolie. I did the same for “Famous women who have had heart disease” which oddly was dominated by men but I found one female name I recognised, Nancy Reagan. To me, it is understandable why women care more about breast cancer than heart disease. It is a disease that is unique to women and to womanhood. It is thus an extremely emotional thing. Heart disease is for all humanity. However emotional the issue of breast cancer may be, the census of the dead shows that female heart disease is ten times that of all female cancers combined. Men also have their emotional links with a cancer that has an incidence rate way below that of heart disease, namely prostate and testicular cancer. Indeed it’s a man thing to grow a moustache for a man’s cancer charity in “Mowvember”.

Rosenbaum explores her explanation in our commitment to cultural groups. It is a distinctive mark of human society that we alone cooperate beyond families and into groups and societies. What we lose as individual or selfish rights, we gain as communal rights[2]. Group identity is central to human society. For a group to thrive, it needs to support and reinforce the very reasons why it is a group. Misfearing is based not on fact but on emotions. It is what keeps opponents of pylons, fracking, intensive agriculture, fast food and the like together. She ends her article thus: ”Certainly, understanding of one’s risk for any disease must be anchored in facts. But if we want to translate into better health, we may need to start talking more about our feelings”.

Years ago during my two decades as a member of the EU Scientific Committee for Food, I learned the difference between fear based on facts and fear based on emotions. The social groups opposed to food additives and pesticides share this common misfear theme and pouring facts into this group is a waste of time. However I might see their “facts” as nonsense or unfounded or disproved, they see them as central and moreover, they see mine as threatening to the central belief of their group.

So how does public health and in my case, public health nutrition, tackle the misfearing among women who wrongly, if facts are the basis of truth, put breast cancer well ahead of heart disease as a threat to their health. Imagine if a mammography test required a prior blood lipid profile test and an ambulatory test? Would that not capture the problems of heart disease in women? Maybe so but the majority of cases of heart disease in women are among the poorer and the more socially disadvantaged. And thus the answer is not so obvious. Diet and lifestyle changes have a far greater link to the reduction in risk of heart disease than they do of most cancers. We need to advertise the fact that for every female death that arises from any cancer, ten times more women will die of heart disease. Simple measures such as blood lipid screening and blood pressure monitoring must be promoted among women.  And the promotion of healthy eating for heart disease prevention needs to gain as much print and social media as that which links diet and cancer, where, like it or not, the strength of evidence is much weaker.

[1] Rosenbaum, L (2014) New Eng J Med, 370, 595-597
[2] Wired for Culture – the natural history of human cooperation” Mark Pagel, 2012, Allen Lane, London