Rain Not to Blame for Joint and Back Pain

December 20, 2017

A commonly held belief has been debunked.

A recent large observational study dismisses the commonly held belief that changing weather conditions lead to increases in joint or back pain.1

Background
Previous studies of the association between joint or back pain and rainfall have resulted in mixed conclusions. However, these studies have been limited by small sample size, problems of recall, and the potential for confirmation bias in surveys.

A research team led by Anupam B. Jena, MD, PhD, Associate Professor at Harvard Medical School in Boston, attempted to address the question anew by analyzing data from millions of outpatient visits. The researchers hypothesized that if a true relation between rainfall and joint or back pain exists, patients might be more likely to seek care for those conditions during rainy periods or, alternatively, mention those symptoms during a previously scheduled appointment that happens to occur during a rainy period. Results were published in The BMJ.

The study
The first dataset included 1,552,842 adults aged 65 or older and insured by Medicare, from the period of 2008 to 2012. The primary outcome of interest was whether each visit included a diagnosis code for a condition reflecting joint or back pain or both.

The second dataset included detailed information on daily rainfall levels by geographic zip code. This information was obtained through the Global Historical Climatology Network Daily database at the National Oceanic and Atmospheric Administration. The data included daily precipitation measurements from 3257 weather stations across the US.

To combine the 2 datasets, researchers matched each Medicare beneficiary’s zip code of residence to the nearest weather station, excluding zip codes farther than 30 miles from a weather station. To explore potential changes in barometric pressure, researchers identified the week of each outpatient visit and generated indicators for the number of days that week that the assigned weather station recorded precipitation. Data were also adjusted to account for patients’ age, sex, ethnicity, and chronic conditions, including rheumatoid arthritis.

The findings
Of the 11,673,392 outpatient visits in the dataset, only 2,095,761 (18%) occurred on rainy days. Thus, researchers were not able to identify a statistically significant relation between visits related to joint or back pain and rainfall, either on the day of the appointment or during the preceding week. Furthermore, no relation was found within the subgroup of patients with rheumatoid arthritis.

“Joint or back pain rates during weeks with seven rainy days were similar to weeks with zero rainy days,” the researchers observe.

Conclusions
The study does have some potential limitations:

• Relying on administrative data lacks the clinical detail to definitively characterize the severity of joint or back pain. It also means that patients with joint or back pain–related conditions that were seen for unrelated symptoms might have had codes for both conditions.

• Researchers also could not detect if patients with increased pain were self-managing pain by taking over-the-counter analgesics.

• Finally, this study focused only on older patients and specifically on rainfall, rather than other weather measurements such as humidity, barometric pressure, or temperature.

As an observational study, no firm conclusions can be drawn about cause and effect. However, in this large dataset, no relation was found between rainfall and outpatient visits for joint or back pain.

“A relation may still exist, and therefore larger, more detailed data on disease severity and pain would be useful to support the validity of this commonly held belief,” the researchers conclude.

References:

1. Jena AB, Olenski AR, Molitor D, Miller N. Association between rainfall and diagnoses of joint or back pain: retrospective claims analysis. BMJ. 2017;359:j5326. doi: 10.1136/bmj.j5326.