Higher relative humidity onset in warm season, and traffic-related pollutants onset in cold season may be associated with a higher odds of migraine headache, according to the results of a study recently published in Environmental International. 

According to the study, 14% (1.04 billion) of adults in the US experience recurrent headache disorders, and weather and air pollution are commonly reported as precipitating factors by patients. 

Air pollution. Source: Getty

“A large number of studies have been conducted to identify triggering factors of migraine, however, the majority relied on participants' self-reported perception regarding potential triggers of migraine headaches,” Wenyuan Li, ScD, from the department of epidemiology at Harvard T.H. Chan School of Public health and the Cardiovascular Epidemiology Research Unit at Beth Israel Deaconess Medical Center, and colleagues wrote in the study. “Several epidemiological studies objectively measured weather data and prospective collected migraine headache events by headache diary, while earlier studies were limited by analytic methods, studies in the past two decades generally agreed that a subgroup of patients with migraine are “weather sensitive”, usually by investigating the associations within each individual.

Using electronic questionnaires, Li and colleagues collected migraine headache onset data from 98 adult patients with episodic migraine from the Greater Boston Area.

The majority of patients included in the study were women and had a mean age of 35 years.

Participants were followed for an average of 45 days across the 4,406-day observational study. 

The researchers obtained temperature, relative humidity, and barometric pressure data from a local weather station. 

Data on daily average fine particulate matter, daily maximum 1-hour sulfur dioxide, daily maximum 1-hour nitrogen dioxide, daily maximum 8-hour ozone, and daily maximum 8-hour carbon monoxide were obtained using local air pollution monitors. 

A repeated measures analysis was conducted using fixed effects logistic regression models. Researchers adjusted for day of week, a natural cubic spline term of day of the year with 4 degrees of freedom, and a participant identifier. Additional adjustments were made for linear terms of temperature and relative humidity in the air pollution analyses. The researchers also applied logistic regression models with generalized estimating equation (GEE) and autoregressive correlation structure in the sensitivity analysis, according to the study.

Li and colleagues found a mean temperature of56.9 °F, relative humidity 67.3%, and fine particulate matter 7.3 μg/m3. 

There was an association between higher relative humidity and higher odds of migraine headache; however, this association was only observed in the warm season (April–September). 

According to the researchers, higher levels of daily maximum 8-hour ozone and daily maximum 8-hour carbon monoxide were linked to higher odds of migraine headache onset in cold season (October–March). 

While no longer statistically significant for relative humidity and O3, logistic regression models with GEE and autoregressive correlation structure led to attenuated results which showed that differing associations by season remained. 

Li and colleagues acknowledge that there were several limitations to the study, including low patient enrollment, low pollution levels in study regions and low variations of exposure levels. 

However, strengths in the study, such as the fixed effect models and sensitivity analyses, warrant further research. 

“Future larger-scale studies with headache diaries and longer follow-up time are warranted to confirm or refute our findings,” the researchers wrote.