‘Bad weather could raise your blood pressure and even kill you,’ is the unnecessarily alarmist headline in the Daily Mail. It reports on a large, complex study that looked for any association between changes in weather and blood pressure rates.
The research focused on patients at a blood pressure clinic in Glasgow and looked at two consecutive visits the patients made within a 12-month period. The researchers combined these findings with Met Office weather data from the time of these visits to assess whether changes in patients’ blood pressure were related to changes in the weather.
They found that decreases in temperature and sunshine, or increases in rainfall and frost, were associated with a slight increase in blood pressure.
In the longer term, individuals whose blood pressure seemed sensitive to decreases in temperature and sunshine had slight increases in blood pressure. They also seemed to have overall shorter survival than people insensitive to weather changes.
We know that our bodies respond to temperature changes, so it is plausible that temperature could influence blood pressure. But factors other than the weather may have had a role to play in the blood pressure results seen.
It is also important to point out that the minor increases in blood pressure detected by the study could in many cases be compensated for by taking more exercise or improving your diet.
Where did the story come from?
The study was carried out by researchers from the University of Glasgow. One of the study authors was supported by a Wellcome Trust Capacity Strengthening Strategic Award to the Public Health Foundation of India and a consortium of UK universities.
It was published in the peer-reviewed Journal of the American Heart Association.
The quality of the Daily Mail’s reporting of this study is mixed. On the negative side, it presents an over-simplistic conclusion that cannot be drawn from the complex analysis used in this study. The claim made in the headline that ‘bad weather…can kill you’ is needlessly sensationalised.
On the plus side, its story does contain useful advice from a spokesperson from Blood Pressure UK: “Until we can control the weather, we can still rely on more traditional ways of controlling our blood pressure, such as eating more fruit and vegetables, less salt and alcohol, and taking more exercise.”
What kind of research was this?
The researchers say that there is growing evidence that outdoor temperature has an influence on blood pressure, with blood pressure being higher in winter and lower in summer.
This is believed to be because the constriction of blood vessels at colder temperatures increases blood pressure. However, it is unclear whether the temperature-related response differs among individuals.
The current study aimed to examine people’s individual changes in blood pressure in response to a range of weather patterns. The researchers also wanted to see whether this was predictive of longer term blood pressure control and mortality.
What did the research involve?
The study included 16,010 people from the Glasgow Blood Pressure Clinic (47% male) who had been referred by their GP in order to control their high blood pressure.
Information on the monthly average weather for the west of Scotland was obtained from the UK Met Office. The Met Office has used a consistent method to analyse climate patterns since 1961, and can provide weather for square kilometre grid points across the UK.
Each visit every person made to the Blood Pressure Clinic was mapped to the mean monthly weather of the west of Scotland. Mean monthly measurements for each of the four aspects of weather were ranked from the lowest to the highest measurement, and then split into four equal groups called quartiles. The lowest quartile (Q1) contained the lowest 25% of measurements and the highest quartile (Q4) contained the highest 25% of measurements.
For each person, the researchers looked at pairs of consecutive clinic visits that were at least one month apart but within the same 12-month period. They were interested in pairs of visits where weather either remained constant (both visits in the same weather quartile) or where weather was very different (one visit in the lowest quartile and one visit in the highest quartile). They categorised the weather for these clinic visits as:
Q1 to Q4, where weather for the first clinic visit was in the lowest quartile and the subsequent visit was in the highest quartile
Q4 to Q1, where weather for the first clinic visit was in the highest quartile and the subsequent visit was in the lowest quartile
Qn to Qn, where both the first and the second clinic visits were in the same weather quartile – there was no change in weather patterns
For each individual, the researchers examined changes in their blood pressure and heart rate between the two visits, and looked at how the size and direction of this change (up or down) related to the change in weather.
The researchers used the General Register Office for Scotland to obtain information on deaths among the participants and causes of death. Mortality information was available up to 2011, allowing up to 35 years of follow-up.
Source: Read More at NHS