Seasonal covariation in physical fitness and blood pressure at rest and during exercise in healthy middle-aged men.

It has been suggested that seasonal changes in cardiovascular risk factors may explain simultaneous seasonal variations in cardiovascular diseases. Since systolic blood pressure (SBP) during an ergometer exercise test adds prognostic information beyond that of BP at rest we aimed to study whether SBP during exercise also demonstrates similar seasonal variation after adjustment for covariates. Blood pressures of 1574 apparently healthy men aged 40-59 years examined throughout two consecutive years showed a seasonal variation, with higher SBP during the period September-December compared with the rest of the year, 2.8 mmHg (p = 0.003) at rest and 4.2 mmHg (p < 0.001) during ergometer exercise at 600 kpm min-1. After adjustment for a parallel marked drop in physical fitness, these differences were no longer significant. Thus, the seasonal variation in SBP at rest and during exercise in apparently healthy middle-aged men may be explained by a parallel seasonal variation in physical fitness. A seasonal covariation in long-term cardiovascular mortality in the same study suggests that the parallel variation of independent risk factors is of clinical significance.