Wednesday, November 28, 2007

Big risk factor contest

boxing match
This match between two unequal opponents, body fat and passive smoking, goes over the full distance of twelve rounds, and there is a clear winner on points.

Background: I have blogged about both subjects that share some aspects like epidemiology and risk statistics but are fundamentally different in many other features. In order to check all again, I am ready for a roundup. I am using a boxing metaphor because of the controversy in both subjects, sometimes with unfair arguments (aka deep hits), hard facts (aka real hits) as well as biased claims (aka futile attacks), and a number of aspects (aka rounds) where both subjects may perform differently, but in the end we should be able to decide which of both, body fat or passive smoking, is the more important risk factor for health.

So let the match begin now, and like a pro match, this one goes over twelve rounds:

  1. Which condition is more prevalent?
  2. How is the actual trend?
  3. How many diseases have been linked to them?
  4. Which of both reaches higher relative risks?
  5. What about the absolute risk of being killed by a disease?
  6. How is the relation between dose (the amount of the risk factor) and response (disease)?
  7. Is there a safe level that is causing no harm?
  8. How is the interaction between the two conditions?
  9. Is there a causality or only a correlation?
  10. Can the effect be explained by biological mechanisms?
  11. What about the integrity of the research and possible conflicts of interest?
  12. Have interventions against the risk factors been successful?
1. Prevalence
In countries without smoke-free regulations in public places, more than fifty percent of the population are exposed to secondhand smoke regularly. In the United States, about thirty percent of the population are obese; in other countries, this amount is considerably lower.
Judge 1: "In many places, the exposure to secondhand smoke has diminished due to legislation, but this is the result of an intervention and must not be taken into account here. The facts are clear, passive smoking is more prevalent than obesity." The other judges agree.
Unanimous verdict: Passive smoking wins the first round.
Reporter: "The audience seems to favour body fat, but the judges obviously are not very impressed by his futile attacks, based on the BMI 25+ definition of overweight, and only count the BMI 30+ obesity as real hits. Passive smoking is leading 1-0."

2. Trend
In many parts of the world, people are getting fatter. The exposure to secondhand smoke, on the other hand, is decreasing because of smoking bans in many public and working places.
Judge 1: "Most countries have ratified the WHO Framework Convention on Tobacco Control. The winning trend is fat." Judge 2: "Fat goes up, secondhand smoke goes down." Judge 3: "Agreed."
Unanimous verdict: Body fat wins the second round.
Reporter: "The optical advantage of the first round has materialized now, allowing body fat to equalize to a 1-1 draw."

3. Number of diseases
Passive smoking has been linked to diseases of the heart and the lungs, to lung cancer and other cancers, and to stroke. Obesity has been linked to the same diseases plus those of digestive tract, kidneys, rheumatic diseases and psychic disorders.
Judge 1: "A clear lead for body fat." Judge 2: "A draw in the big killers, and there is poor evidence for causality in the body fat." Judge 3: "Causality is of no concern in this round, only the number of diseases linked to the risk factors, and this number is considerably higher for body fat."
Split verdict: Body fat wins the third round.
Reporter: "After a bad start, body fat is gaining the upper hand now, leading 2-1."

4. Relative risk
Extreme obesity has been linked to relative risks of 2 and more for various diseases, compared to only 1.3 on average in the case of passive smoking.
No dispute among the judges.
Unanimous verdict: Body fat wins the fourth round with a big lead.
Reporter: "This time, the judges agree with the audience. Body fat has been the darling of the media and it seems that he is living up to the reputation now, pulling away by 3-1."
References: Passive smoking math, body fat math

5. Absolute risk
Both factors, passive smoking as well as body fat, have been linked to the big killer diseases like heart attacks and cancer who also have the highest lifetime risks: Every second man and every third woman will be affected by one of these diseases.
Judge 1: "I would weigh body fat higher for disease number and relative risk but these have already been judged in rounds three and four, therefore a draw." Judge 2: "I would weigh passive smoking higher because of better causal evidence but this will be judged in round nine, therefore a draw." Judge 3: "Draw."
Unanimous verdict: Draw.
Reporter: "Passive smoking is trying hard for not losing, but it does not look good for him. Body fat maintains his lead by 3-1."

6. Dose-response
Lowest levels of secondhand smoke are linked to lowest risk of disease, and the curve is steady and /-shaped, and there is no optimal level of secondhand smoke. Lowest levels of body weight, as well as highest levels, are linked to higher risk of disease, and the curve is J- or even U-shaped, and there is something like an optimal level, called the ideal weight.
Judge 1: "Secondhand smoke is a risk factor in its strict sense but body fat is not." Judge 2: "Too low body fat may also be a risk factor, weakening the punch of body fat." Judge 3: "Very strong straight jab wins against weak hooks."
Unanimous verdict: Passive smoking wins the sixth round.
Reporter: "Oops this has been clear but body fat is still ahead by 3-2."

7. Safe level
There is no safe level for secondhand smoke, even small amounts do harm. On the other hand, body fat is not a risk factor but a vital element. No discussion.
Unanimous verdict: Passive smoking wins the seventh round.
Reporter: "Body fat is groggy, tumbling. Oh, oh, oh. A bad weakness has been hit. We see a 3-3 draw now, and passive smoking is gaining momentum."
Reference: The vital importance of body fat

8. Interaction
For active smokers, and most likely for passive smokers as well, higher levels of body fat seem to be protective rather than harmful. Thus, smoking as a risk factor weakens body fat as a risk factor. No discussion.
Unanimous verdict: Passive smoking wins the eight round.
Reporter: "Both have been in clinch, but passive smoking wins the infight and is leading now by 4-3."
Reference: Positive outcomes linked to body fat

9. Causality
The noxious substances from secondhand smoke are most likely the causes of harm. Body fat is not at the beginning of a causal chain but somewhere in between, the causality remains unclear. No discussion.
Unanimous verdict: Passive smoking wins the ninth round.
Reporter: "Body fat is on the ropes. The score is 5-3."
Reference: Storks and babies, fat and cancer cells

10. Biological mechanisms
The mechanisms leading to artery disease and cancer are well-understood in the case of fine dust and mutagenous substances from secondhand smoke but not so in the case of body fat. No discussion.
Unanimous verdict: Passive smoking wins the tenth round.
Reporter: "This hurts. A clear lead by 6-3."

11. Integrity
Big Tobacco has tried to undermine secondhand smoke research. Big Food, as well as Big Pharma, make a lot of profit with weight loss.
Judge 1: "Refutations of passive smoking results are deep hits and must not be counted." Judge 2: "Body fat has been doped by Big Pharma." Judge 3: "Obesity denial is deep hit of fast food chains and must not be counted."
Split verdict: Passive smoking wins the eleventh round.
Reporter: "This is the end of the story. 7-3."

12. Intervention success
Smoking bans have reduced harm from passive smoking to a measurable extent. The success of weight loss attempts is poor, resulting in yo-yo and failing to show a positive effect on health in most cases and if so, it may be due to better fitness or healthy food or metabolic changes rather than reduced body fat. No discussion.
Unanimous verdict: Passive smoking wins the last round.
Reporter: "Body fat had some strong rounds in the beginning, but the weaknesses have been too obvious. On the other hand, passive smoking has shown to be a true risk factor that must be respected. A clear win on points by 8-3."
Reference: About a mechanism of yo-yo

Photo credit: Wikipedia

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