We agree with the comments made by Ivy Shiue. The potential for meteorological variables to influence risk of stroke and myocardial infarction is clear and must be considered further. There are plausible biological mechanisms through which this may occur and should predictions regarding climate change prove accurate, these may become more important in time. What remains entirely unclear is the nature and magnitude of the impact of such factors. For example, some studies suggest increase in ischaemic stroke risk with lower ambient temperature (1) while others suggest an increase with higher temperature (2). Similar differences exist regarding risk of myocardial infarction and furthermore, these relationships may not be consistent, either across stroke subtype, geographical area or patient group.
We therefore agree that establishing the true relationship between climactic variables and vascular risk will prove difficult. For example, regarding stroke, we hope to identify an association between heterogeneous meteorological variables and risk of this multifactorial and heterogeneous disease.
We echo the comment that carefully designed studies are required, with appropriate consideration of potential confounding variables. The phrase ‘real world’ complexities could not be more appropriate and we do not believe the current literature is able to sufficiently consider such complexity. Progress is however being made. Our aim should be to generate sufficient information to allow public health advice to be given which protects the vulnerable during, for example, periods of temperature flux. Recent data by Bhaskaran et al. (3) goes some way; they found the elderly with established ischaemic heart disease who were not taking aspirin were at particularly high risk on cold days. However, in common with other studies to date, the methodology did not allow for study of the actual temperature to which patients were exposed; an important source of potential confounding in societies where most have access to heating systems and cooling devices.
We welcome this discussion and hope that we move towards asking more specific questions than simply ‘is the weather important?’ The case for this is largely made and more clinically relevant questions, which can guide public health strategies, require to be asked.