Among the research articles published in this issue, are some surprising results and statements. Here we present synopses of a few, which include the effects of tobacco – one of the main discussion subjects at the international gathering of cardiologists in Barcelona, this September
Previous studies have shown that tobacco smoking increases the risk of heart disease. However, to date most of those studies have been in developed countries, and few large studies have been carried out to examine the effects of tobacco in other geographical regions.
Results from the INTERHEART study have led Professor Salim Ysif, of Hamilton General Hospital-McMaster Clinic, Hamilton, Canada, and Koon Teo, of McMaster University, Ontario, Canada, and colleagues, to conclude that all forms of tobacco exposure, including smoking, chewing or inhaling second hand smoke, increase the risk of heart attack up to three times.
The team calculated the risk of heart attack for various forms of active tobacco use (both smoking and non-smoking) and second hand smoking (SHS) in all areas of the world. The study included data from over 27 000 people in 52 countries. The investigators adjusted their calculations to exclude the effect of other lifestyle factors that could affect heart attack risk, such as diet and age.
They found that tobacco use in any form, including sheesha smoking, which is popular in the Middle East and beedie smoking, common in South Asia, was harmful.
‘Chewing tobacco also increased the risk of a heart attack two fold, indicating that all forms of tobacco use or exposure are harmful,’ added Dr Koon Teo.
Compared with people who had never smoked, smokers had a three-fold increased risk of a heart attack. Even those with relatively low levels of exposure (8–10 cigarettes a day) doubled their risk of heart attack.
However, the researchers did find that the risk of heart attack decreased with time after smoking cessation; among light smokers (<10 cigarettes a day) there was no excess risk 3–5 years after quitting.
By contrast, moderate and heavy (20> cigarettes a day) smokers still had an excess risk of around 22%, 20 years after quitting.
The team also found that exposure to second hand smoke increased the risk of heart attack in both former and non-smokers. The findings suggest that individuals with the highest levels of exposure to SHS (22 hours or more per week) may increase their risk of heart attack by around 45%.
‘Since the risks of heart attack associated with smoking dissipate substantially after smoking cessation, public-health efforts to prevent people from starting the habit, and promote quitting in current smokers, will have a large impact in prevention of heart attack worldwide,’ Professor Yusif concluded.
BMI cannot predict outcome for HD patients
Physicians know that obesity is a risk factor for developing heart disease. However, just how obesity affects people with established heart disease has remained unclear because studies have produced contradictory results, until now.
According to new study results reported by Francisco Lopez-Jimenez, and colleagues at the Mayo Clinic College of Medicine, in Maryland, USA, body mass index (BMI) - a number calculated from a person’s height and weight, which is commonly used as a measure of obesity - cannot reliably predict the outcome for patients with heart disease, because BMI is an unreliable indicator of obesity.
To investigate, the researchers combined data from 40 studies, involving about 250 000 people with heart disease; the average follow-up was four years. Most of the studies used BMI as a measure of obesity. The investigators found that patients with a low BMI had a higher risk of death than those with a normal BMI. Overweight patients had better survival and fewer heart problems than those with a normal BMI. Obese people who had had bypass surgery had a higher death rate when compared with people with a normal BMI, while severely obese people had a higher risk of a heart-related death but not death from other causes.
Underweight = <18·5
Normal weight = 18·5-24·9
Overweight = 25–29·9
Obesity = BMI of 30 or greater
The better outcomes for overweight people might be because they have more muscle than normal weight people, the authors said. They concluded that the results therefore demonstrate the inability of BMI to discriminate between body fat and lean muscle. ‘Rather than proving that obesity is harmless, our data suggest that alternative methods might be needed to better characterise individuals who truly have excess body fat, compared with those in whom BMI is raised because of preserved muscle mass,’ Dr Lopez-Jimenez explained.
In an accompanying Comment in The Lancet, Maria Grazia Franzosi, of the Istituto Mario Negri, Milan, Italy, said: ‘BMI can definitely be left aside as a clinical and epidemiological measure of cardiovascular risk,’ adding: ‘Uncertainty about the best index of obesity should not translate into uncertainty about the need for a prevention policy against excess bodyweight, which must be strongly supported.’