The weather-headache nexus

name. With so many people reporting that changes in the weather trigger a migraine or tension-type headache attack, the headache-weather link is a perennial topic of interest. In some studies, as many as 70 percent of subjects report a causal link between weather conditions and their headaches. So no wonder numerous studies have set out to establish once and for all whether there are significant associations between weather and headache, and, best case, identify definite correlations that would explain them.

Research theory and practice

Many of these studies are designed the same way. People with migraine or tension-type headache record the details of their attacks in a headache diary over a specific period of time. Over that same period, researchers keep track of weather data (air pressure, temperature, humidity, wind movement, etc.) sourced in most cases from the nearest weather station. The researchers also record dynamic processes such as drops in atmospheric pressure and rising temperatures, since a lot of people link their attacks to changes in the weather. A tremendous amount of data is collected in this way.

Then, using mathematical and statistical models, patient headache diary records are compared to specific local weather parameters at those times and combinations thereof (e.g., atmospheric pressure and temperature). The purpose of all this number crunching is to discover any statistically significant, robust correlations between certain combinations of weather phenomena and headache events.

So much for the theory, based on which you would expect similar procedures to produce comparable results. In practice, the results turn out to be remarkably heterogeneous. Some studies see no relation at all. Others identify minor correlations at best. In any event, the science in this field is remarkably inconsistent compared to hard science research in other areas. Still, let’s have a brief look at some of the studies.

Some study results

A study at Charité hospital in Berlin cross-checked the headache diaries of migraineurs against weather data including 4-hourly temperature and atmospheric pressure (barometric) data over a period of one year. In six patients, a statistically significant correlation was found between migraine attacks and weather phenomena; specifically, a drop in temperature with a simultaneous increase in humidity. No other correlations were detected.

Genetics, the "silent" factor

In their discussion of the results, the authors consider whether genetic confounders might play a role. Are there individuals in the study population whose genetics make them more sensitive to patterns or changes in the weather, the authors ask. That would explain why significant correlations were found in just one subset. Nonetheless, the study reveals how difficult it is to say anything for sure when factors such as the subject's current state of mind, genetic predisposition, and physically measurable weather data are all in play at the same time.

The authors cautiously propose that there may indeed be a sub-population of migraine patients whose genetics make them more reactive to weather phenomena than the rest of the population. This would also neatly explain the striking inconsistency between different – but similarly designed – studies. Ignoring genetics when selecting subjects might give rise, quite by chance, to groups with wildly different or identical genetics, and these unknown factors would affect the results of the research.

Inconsistent evidence

A University of Vienna in 238 migraineurs asked participants to keep a diary for 90 days and enter details on 59 items on each of those days, including subjective weather perceptions. Upon statistical analysis, it first seemed that there were some correlations. After multivariate analysis (correction for multiple testing), the findings were no longer significant. This is another example of a very common phenomenon in research. A very large proportion of patients will be absolutely clear in their own minds that (a change in) the weather gives them a headache. But at the end of the day, these are subjective perceptions that rarely stand up to scientific scrutiny.

As already stated, the evidence is inconsistent and there is always another study that says the exact opposite. In 2011, Kazuhito Kimoto at Dokkyo Medical University in Mibu, Japan, published a study in migraineurs confirming a link between migraine attacks and barometric pressure. Static pressure did not have an effect. Instead, migraine attacks occurred more frequently – in 18 of 28 patients studied – when barometric pressure was more than 5 hPa lower from one day to the next.

Discrepancy between what people sense and what the data shows

Research by Prince, Rapoport et al at Yale University School of Medicine in Connecticut, USA, also found a statistical correlation between one or more weather phenomena and migraine occurrence in some subjects. However, far more subjects thought they were sensitive than were actually found to be sensitive to weather. In addition, factors other than self-reported triggers were found to have an effect. So there was a clear but ultimately unexplained discrepancy between perceived connections and demonstrable correlation.

So what is the truth?

Few areas of research produce a more mixed bag of results and contentious claims than the headache-weather connection. If you believe science can shed reliable light on what’s going on here, think again. There are too many variables involved and everyone’s subjective perceptions are different. Without a doubt, our bodies react to the weather. And some people are more sensitive to a change in weather than others. But that’s about all anybody can say for sure.

Sensitivity to the weather may also be partly due to the fact that our bodies are out of practice and no longer able to respond fast enough to different weather conditions, or (more importantly) in the proper physiological manner using the right physical processes – to quote Angela Schuh, a professor of medical climatology at Ludwig-Maximilians-Universität (LMU) Munich in her book “Biowetter” [“Bioweather”]. The author also points out that most people these days work indoors, get too little daylight and lead irregular lives. This "de-rhythmization," as Schuh calls it, might also play its part in causing headaches associated with weather sensitivity. Which brings us back to the conclusion that a multifactorial process is involved that largely eludes elucidation with the tools of natural science.