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September 2012

Childhood obesity is bad news for heart disease in the future

Carl Heneghan
Last edited 26th September 2012

Apart from stating the obvious, we are in big trouble. Health services costs are rising and we can’t afford it. There are no new drugs to counteract the growing increase in chronic disease which cost us a fortune. Yet, to counteract all this we are getting fatter and fatter, and presenting a future steeped with dire consequences for our children.

Results from 63 studies of 49,220 children aged 5 to 16, published in today’s BMJ by our group, starkly illustrates the effect obesity has upon increasing risk of cardiovascular disease for future generations of children. We know that being overweight in adulthood increase your risk of heart disease and stroke, we now know that for children, these very same risk factors are increased markedly at a very young age.

Obese children have a blood pressure greater by 7.5mmHg than normal weight children. This rises to 11.5 mmHg when the more accurate ambulatory blood pressure readings are used. The increase seems to be greater for girls than boys: but the reason for this additional increase is unknown. Also, other important risk factors for heart disease are raised in obese children: blood lipids (cholesterol and triglycerides) are raised; fasting insulin and insulin resistance are worse and the left ventricular mass of the heart is increased when compared to normal children.

Being overweight as a child corresponds to a Body Mass index (BMI) of 25 to 30 and obesity as a BMI of over 30. BMI is a number calculated from a child's weight and height, and is weight in kg divided by height in metres squared (kg/m2). Although BMI does not measure body fat directly, it correlates with accurate measures of body fat, such as underwater weighing, and can be used as a simple measure for screening children.

Many countries use reference points in children to classify obesity, taking into account age, sex and a reference population. Whilst this data calculates an average for the population, and classifies obesity according to the degree of variation from this mean it may mask worrying trends due to increasing average weight of children over time. In 2007, the US obesity rates have nearly quintupled among 6- to 11-year-olds since the 1970s. Worryingly, in the UK school year, 2010/11, one third of children aged 10 to 11 were overweight or obese.

Like climate change, we know the problem is coming, but because the effects are at some point in the future, we are burying our heads in the sand, hoping the problem might just go away. For what is an easy situation to prevent: we need concerted action now. Jamie Oliver, once said "we're losing the war against obesity," We may have already lost it: 1 in 3 adults and 1 in 6 children are currently obese.

Let’s be honest. Most researchers and clinicians only read the abstracts of research studies. This is true even when they diligently search out and find the original article that inspired a news headline. A cynical colleague suggested that people only read the Tweets of someone that only read the abstract of the article. People are busy and pressed for time; skimming abstracts is an efficient way to stay up-to-date with research findings without onerously sifting through pages of details. People want the bottom line. But this approach inherently relies on journals to ensure accuracy in abstract reporting.

Well, it seems this strategy is problematic for many reasons, particularly because of “spin” or “specific reporting emphasizing the beneficial effect of the experimental treatment.” A recent study in PLoS Medicine sought to quantify this problem: the authors identified two-arm, parallel-group RCTs, searched for associated press releases, and examined both for the presence of “spin.”

What they found was concerning: 47% of press releases and 40% of abstracts contained “spin.” After completing a multivariable analysis, “spin” in the article abstract was the only factor associated with “spin” in the press release (RR, 5.6; CI, 2.8-11.0; P<0.001). Therefore, the major driver of inaccurately reported findings was written by the author. In fact, 31% of press releases misinterpreted the results from the trial, either over- (86%) or under- (14%) estimating the benefit of the therapy.

Press releases are an important part of research dissemination. A study completed earlier this year in the BMJ by Evidence Live Faculty Lisa Schwartz and Steve Woloshin found that high quality press releases by journals can influence media coverage of the associated article. Increased coverage is beneficial if the press release is accurate which relies heavily on the abstract.

People involved in conducting research understand the importance of the abstract. This is the first piece read by a journal editor once submitted, and the decision to peer review largely relies on the authors ability to ‘sell’ their study in 300 words or less. Therefore, there is an incentive for authors to (over) emphasize the main results of the study in a manner that is usually critiqued in the peer review phase. While changes may be made to the full-text article to “dumb down” the authors conclusions, it is unclear how much the abstract changes as a result of peer review.

Realistically, the previously described process is unlikely to change, and everyone is not going to start reading the full-text article, particularly the media. Therefore, the onus is on journals to take an active role to ensure accuracy in abstract reporting and press releases. If they don’t, who will? If you want to learn more about what journals are doing to tackle this problem, come and ask the editors yourself at Evidence Live 2013.

*Note: this blog has also been posted on Evidence Live Blog.

Why bringing home the bacon isn't always the best thing

Kamal Mahtani
Last edited 14th September 2012

We consume too much salt. The problem is that high salt levels are associated with increased blood pressure and therefore increased risk of heart disease and stroke. Although the government says we should be consuming no more than 6 grams per day, we probably consume about 9 grams per day. The majority of that salt comes from processed foods rather than from adding salt at the table. Now a new survey from the UK based "Consensus Action on Salt & Health" (CASH) reveals what most lovers of a bacon sandwich probably don’t want to hear. Bacon has superseded ready meals, as the second highest contributor to salt in our diet with, in some cases, just 2 rashers providing half the total recommended daily amount. The survey reviewed the salt content of over 120 bacon packs available from high street supermarkets and found wide variations in bacon salt levels within the same supermarket. For example the supermarket Morrisons sells a Savers Smoked Rindless Back Bacon product with 6.8g salt per 100g bacon while also selling a different own brand pack with 2g salt per 100g. The CASH website has posted an industry response from Morrisons reporting that the supermarket will be targeting lower salt bacon products in the New Year.

So if bacon is the second highest contributor to salt, what is the first? I’m afraid it’s the bread holding your bacon sandwich together. Pre-packed bread and rolls remains the number 1 contributor to salt in the UK diet. The rest of the list includes fat spreads, cheese, sausages, cereals, ham and morning goods.

Hmmm….I think I’ll stick to my porridge for breakfast from now on.

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