MPH Master pieces

A triplet of weight loss

This week not one, not two, but three trials of programmes for weight loss.

It's difficult to get one's head around so much information, but the PICO approach can help: for each paper get clear in your mind (ok, so put it on a piece of paper) the

Target Population (e.g. Body Mass Index > 30 / BMI >30 plus other risk factors)

Exact Intervention (group sessions / telephone support etc )

Comparator and

Outcome (weight loss at 3 months / 24 months etc).

Ideally you would wait for a systematic review to put it all together but we don't always have that luxury: we need to make up our own minds now.

A question raised by all of these trials is whether a weight loss of, say, 5% is worth having. In public health we tend to take the view that even small changes can add up to huge benefit at population level. The concept of '"minimal important difference" is taken very seriously in planning clinical trials: the smallest difference which is worth having from the patient's point of view.  

Alcohol in Cali

It seems that there is no problem so bad that alcohol cannot make it worse.

Cali, Colombia has one of the highest murder rates in the world: 68 per 100 000 in 2008. Just pause for a moment to think what that would mean in your own home town.

At various times during the period 2004 to 2008, depending on political will, alcohol sale and consumption in Cali was prohibited from either 2am, 3am or 4am till 10am. A simple analysis (see fig 2) displays homicide rates according to whether the policy on the day of the homicide was lax (2am), moderate (3am) or strict (4am). The results seem pretty clear but there is also an appropriately complicated time series analyses to take account of various other possible explanations (confounders).

Weight watchers works

How to lose weight? This trial compares Weight Watchers (12 months free membership) with 'usual care' in slightly obese adults (BMI 27 - 35). Design and execution of the trial look good. Weight loss was modest (5kg) and dropout rates high, which is typical of weight loss programmes.

Kate Jolly and Paul Aveyard have written a good commentary. I'd add two further observations:

1. the comparator was 'usual care' but this was a multinational trial. 'Usual' in the UK is not the same as 'usual' in Germany whihc is not the same as 'usual' in Australia.

2. the trial was funded by Weight Watchers 'via a grant to the MRC'. That's probably ok but what would we have said if this was a drug trial funded by the company that made the drug?

 

 

Don't drop dead!

Modify your risk of sudden cardiac death - don't smoke (obviously); BMI between 21 and 25; eat a Mediterranean diet (veg, grain,nuts, fish and daily alcohol); and exercise 30 minutes each day at 3 - 6 METs. At least if you are a nurse. 

Here is the study - worth a careful read. I think its main value is to show just how much depends on lifestyle. What would be your guess on how much your chances of a heart attack decrease if you keep to the four rules above? Though admittedly the diet and (even more so) the exercise rules are quite tough. 

Notice how each variable was measured. Also notice that of the 120 000 nurses in the cohort only 80 000 are included in the study, mostly because of non-completion of the diet questionnaire. I'm not sure why they focussed on sudden death rather than all death from cardiovascular disease. 

Advertising food to children

Not much to say about this one other than - gulp!

Wrong again!

I wrote this blog about four years ago:

Wednesday, August 08, 2007

Fat friends

Another product from the Framingham study! It's difficult not to be wowed by the video attached to web version of this piece - but we need to check the underlying science is sound.  The basic message is that obesity is not just about you, it's about your friends and neighbours. Another reminder of why do public health - man is a social being and influenced by social processes.

Social processes are difficult to measure, which means the statistics can be incomprehensible: and incomprehensible means potentially seriously misleading.

[...]

In this case, we have to take comfort in the fact that the analysis is published in the NEJM. It's the world's leading biomedical journal so I guess they can call on some seriously competent referees.

It turns out that my note of caution about the statistics was well founded and my trust in the NEJM less so: see this critique of the paper.

Bottom line - beware complex statistics, always look at the raw data. And look out for critiques. (Incidentally I'm still waiting to see any kind of critique or response to that odd paper on salt intake I blogged a few weeks ago.)

 

Salt

Standard doctrine links high salt intake to high blood pressure, and high blood pressure to stroke. But  this paper produces an astonishing result: 

"Among 3681 participants followed up for a median 7.9 years, CVD deaths decreased across increasing tertiles of 24-hour sodium excretion, from 50 deaths in the low (mean, 107 mmol), 24 in the medium (mean, 168 mmol), and 10 in the high excretion group (mean, 260 mmol; P < .001)"

That's the opposite of what's supposed to happen, and contradicts the well established Intersalt studies. And as the authors point out, if their finding is true it undermines the rationale for reducing salt in our diet.

As with any study we can make our own critiques (e.g. only 1499 of 3681 participants included) but the conclusion is so important that we need to hear from experts in the field. In fact I'm surprised that the JAMA did not commission a covering editorial or commentary.

For now:

(1) I'm pretty sure that high blood pressure predicts stroke.

(2) Several intervention studies have shown that low salt diets lower blood pressure.

(3) I never add salt my food, make my own bread (the bread you buy is a major source of salt), avoid high salt foods and am very happy with what I eat. Low salt is not a penance!

But (4) this has taken me back to the influential Intersalt reports, which were based on a much larger sample (10 079) with a much wider range of sodium excretion. But these reports don't say quite what I thought they said - moral: always check your references!

The first Intersalt report showed that the small number of extreme societies with very low sodium output had low mean blood pressure; in more typical societies, urine sodium didn't predict mean blood pressure but it did predict how steeply blood pressure would rise with age.

The second Intersalt report reanalysed the same data and showed that urine salt excretion does predict both mean blood pressure and how steeply it rises with age. This second report unhelpfully added some strongly worded conclusions about dietary salt intake - they may have been sensible conclusions but what was studied was sodium excretion not salt intake, and they provided no citations on the link between dietary salt intake and urinary sodium excretion. 

 

 

BMI aged 17 and coronary disease in middle age

This paper is pretty impressive. It documents the relationship between BMI at age 17 and the chances of coronary heart disease over the next twenty years or so. Plenty of studies have attempted that but in this one (a) height and weight were measured, not self report and (b) the coronary disease was angiography-proven, stenosis of more than 50% in at least one coronary artery. And in case you are worrying that they may have missed one or two cases, (c) every participant had regular treadmill stress tests after their 35th birthday.

You don't get all that, of course, in an ordinary normal population of volunteers - this data was gathered from members of the Israeli Defence Force.

The conclusion was that even slight overweight at age 17 predicted trouble in the coronary arteries in early middle age. The authors make the point that this occurred at a level of BMI considered 'normal'. One of the functions of epidemiology is to give us the full picture of a disease, and as so often happens what we regard as 'normal' is not necessarily healthy.

Overweight: India vs China

Here is a straightforward piece of descriptive epidemiology with a most intriguing result. In short, in Indian and Bangladeshi populations, but not Chinese, Korean and Japanese there was no evidence that a high body mass index is associated with increased mortality. But we must think very carefully before deciding that overweight is ok if you are from the Indian subcontinent! One possibility is that high BMI in India means you are rich, and that this outweighs (as it were) the disadvantage of obesity.

One moral of this tale is not to take anything for granted - you might have thought this study not worth doing because it is so well established from so many studies in so many places that high BMI means higher mortality.

A Christmas gift?

I am unable to resist suggesting the Mandometer as a Christmas present for someone you know... But the paper is also an excellent account of an RCT, with careful attention to measurement issues, good description of the comparator state and compliance handling.

Meanwhile we continue to add brick by brick to the wall of knowledge about obesity control. Here is a paper from Rhode Island USA with impressive results but in a highly selected population. The interesting concept here is to get people to sign up for weight loss as a team, so that the teams compete with each other for success. Visible and public markers of progress do seem to motivate people, at least in the USA.