Strengths and limitations
The strengths of this study include the large population, the
long follow-up period and the detailed characterisation of the
cohort. Furthermore, all cases of HF were validated, limiting
the inclusion of false positive cases.
As some of the established HF risk factors are included in
the definition of metabolic syndrome, the bar is high for
evidence of an independent effect of metabolic syndrome on
HF incidence. Nevertheless, we chose this approach to mimic
the clinical situation, in which the status of the established
risk factors is presumed to be known. Consequently, robust
statistical methods that can handle some collinearity were
used. The clinical perspective was also the reason for
modelling the established risk factors as dichotomous
variables, as this is how they are handled in clinical decision
making.
This study has some limitations. As we examined only men
of the same age with a similar ethnic background, this study
has an unknown generalisability to women and other age
and ethnic groups. Non-hospitalised patients with milder HF
were not included in our end point, which would tend to bias
the results towards the null hypothesis. Furthermore, as this
study was initiated in the 1970s and the HF diagnosis was
based on a review of medical records, it was not possible to
distinguish between systolic and diastolic HF, as echocardiography
was not available at the time of diagnosis for many of
the patients. Another limitation of the study is that we used
the presence of an interim myocardial infarction during
follow up as a proxy for coronary heart disease. Even if this is
an established method for examining ‘‘non-ischaemic’’
HF,29 30 it would be assessed better in a more specific way—
for example, by examining all participants with coronary
angiography. However, this is not a feasible option in a large,
population-based epidemiological study. Furthermore, we
believe that the presence of a symptomatic myocardial
infarction is a good proxy for coronary heart disease, as it
includes patients with the most advanced coronary heart
disease