Monday, June 20, 2011

Inverse epidemiology

It is a common knowledge that high body weight, high blood pressure, high blood sugar and high blood cholesterol are detrimental to health. In epidemiological studies (studies of disease in the community) the higher these are the higher the illness (morbidity) rate and death (mortality) rate. Put in a different way the lower they are the lower the illness and death rates. The relationship is a direct relationship. But is that always the case? Do illness and death rates go on decreasing with decreases in these variables without limits? Is a body weight of 40 kg. better than a body weight of 60 kg. or a blood pressure of 70/30 better than 100/60? Obviously not. A decrease in these variables is associated with a decrease in illness and death rates within certain limits. After reaching optimum levels the relationship becomes inverted and lower figures are associated with higher illness and death rates. The epidemiology is now inverse (so called).
I must say I came across the term “inverse epidemiology” for the first time when reading about the relationship between blood pressure and cardiovascular outcome in patients with end stage renal disease on maintenance hemodialysis. I am not sure of the use of the term in the general sense I described earlier. But it seems to me it applies just the same outside the situation of patients on dialysis and outside the subject of blood pressure.
In fact it also applies to aspects of life outside the field of medicine. Direct relationship becomes inverse after certain limits. Too rich, too powerful, too beautiful etc. may become a curse rather than a blessing!!

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