Nighttime leg cramps commonly affect adults over the age of 50, but are also known to occur in younger adults and children. While their cause is unknown, a study from the University of Alberta's Faculty of Medicine & Dentistry is shedding new light on the painful condition.
"Most doctors will be surprised to learn that this condition is seasonal," says Scott Garrison, the study's principal investigator and an associate professor in the Department of Family Medicine. "For us the greatest surprise came in just how strong that relationship was. From our data it looks like the burden of cramp symptoms may roughly double in the peak of summer, compared with the mid-winter low."
The findings have been published in the January edition of the Canadian Medical Association Journal. As part of their study, researchers tracked the number of new quinine prescriptions (a drug commonly prescribed to treat leg cramps) for adults over 50 years of age in British Columbia, Canada, from Dec. 1, 2001 to Oct. 31, 2007. Over that time period, there were 31,339 people who began taking quinine, 61 per cent of whom were female. The researchers then also examined the number of Google searches over an eight year period that originated in the United States and Australia for leg cramps.
It was found that prescriptions for quinine peaked in British Columbia in July, as did Google searches in the United States for the term "leg cramps". Google Trends data indicated a similar peak for the search term in Australia in the month of January, which is near mid-summer in the southern hemisphere.
Garrison says that, while there have previously been anecdotal reports of pregnancy-associated leg cramps being worse in summer, the findings establish the phenomenon of seasonality in leg cramps in the general population. It's not known why this is the case but Garrison suggests there may be subtle aspects to human physiology affecting the condition that are not yet fully understood. More research is needed.
The findings could have implications for clinical practice in countries (e.g., Canada and the United Kingdom) where quinine is still in widespread use for the prevention of nocturnal leg cramps despite safety warnings.
"While quinine works for some people, it comes with significant risk of toxicity," says Garrison. "Rather than taking quinine every day to prevent cramps during the night, it may be possible for patients to stop taking their quinine in the six colder months of the year when their cramps may not be as bad. Understanding why your symptoms are getting worse also helps you to cope with them."
The study was funded through the Therapeutics Initiative's Pharmacoepidemiology Working Group, as part of the British Columbia Pharmacovigilance Project. Garrison was funded through a Doctoral Fellowship award from the Canadian Institutes of Health Research (CIHR - Institute of Aging).