With April showers in the forecast yet again for Thursday in the Philly region, joint pain “is likely to be severe and last longer.” More pain is possible Friday.

That’s according to the outlook posted Wednesday on the Arthritis Foundation website. But patient discretion is advised, says Mike Doll, senior meteorologist with AccuWeather Inc., which is the source of the forecast — sponsored by Tylenol on the company’s website, by the way.

Dr. Algorithm, informed by research that has linked atmospheric variables to pain onset, is the author of those prognoses.

While the studies haven’t been conclusive, patients through the years have lent support to the notion that they are on to something.

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“Weather does impact pain in many patients,” Brett L. Smith, a rheumatologist who practices in Tennessee, said last week. Complaints appear to run highest with changes wrought by approaching and passing storms and frontal systems, traffic that is quite common in April.

But no one has been able to determine precisely how or why the weather might induce pains or why so many of the estimated 60 million Americans who endure arthritic-related chronic joint torment appear to be immune from the rains.

It was 60 years ago that University of Pennsylvania arthritis expert Joseph Hollander first affirmed that he had found the weather-arthritis connection with a science-fiction evoking experiment in which his patients inhabited a climate-controlled apartment called a Climatron.

In the decades since, studies have both affirmed and questioned the linkages.

That the weather affects the human body is indisputable. Along with the obvious impacts of sunshine and extreme heat and cold, research has linked it to ailments ranging from migraines to asthma to flu incidence, to a vast host of other afflictions.

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But the human body and the atmosphere form one of the most complex intersections in the known universe, and arthritis research is a classic case study of the frustrations in verifying weather-health connections.

Climatron

The conditions inside Hollander’s Climatron were exquisitely spring-like. The temperature was 76, the air comfortably dry and scrubbed clean. But the weather inside was about to get frightful.

He was on a mission to settle the debate. “I must agree that this ‘weather effect’ is not just another old wives’ tale,” wrote Hollander — a self-described weather-sensitive arthritis sufferer — in a paper describing his experiment.

His volunteers spent two to four weeks, two at a time, in a 270-square-foot sealed apartment built inside the Hospital of the University of Pennsylvania.

For the first five to seven days, Hollander kept conditions constant. To simulate the approach of a storm he increased the humidity, or moisture content of the air, and varied the air pressure, or weight, over six-hour periods. He didn’t alert the patients, who were to keep diaries of their sensations.

With the changing environment, seven of the eight subjects experienced “significantly worsening” pain during most of the exposures.

But not every time. And in a mystifying result — the type of cosmic hiccup that has bedeviled the pursuit of connections between the weather and human physiology — one of them was absolutely asymptomatic.

That was all the more perplexing given the pressure extremes.

A word about pressure

Barometric pressure has all but evaporated from the public consciousness these days, but it is a critical weather variable and anyone who has experienced pressure change with altitude knows what a profound effect it can have on the human body.

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When the pressure is high and the air heavy, the weather tends to be fair as descending currents discourage clouds. When a storm approaches, the air becomes lighter, symptomatic of rising air parcels that condense into rain and snow.

Even with a storm’s passage, the changes in pressure usually are gradual and quite subtle, on the order of 1% to 2% over 24 hours. Climatron’s were several times larger, and in just six hours. In fact, the difference would be perhaps 10 times greater than the pressure change at the center of a developing “bomb cyclone.”

About pain

The Arthritis Foundation, a research and advocacy group, has identified 100 different types of arthritis. Joint pain can result from wear and tear, inflammation, or an abnormal immune response.

Even subtle changes can trigger pain, said Brett Smith, who is with the Blount Memorial Physicians Group, Rheumatology, in Maryville, and East Tennessee Children’s Hospital, in Knoxville.

“My suspicion on mechanism has to do with pressure receptors in nerve endings,” he said. With arthritis or after a physical injury, “those nerve endings don’t function normally and begin firing with less stimulation.”

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Another hypothesis holds that pain results when rising and falling pressures cause tendons and scar tissue to contract or expand.

“I think people’s joints are like elevators,” he added. “We can definitely feel the change in acceleration or deceleration, but we don’t feel it when we are at a steady speed in the elevator. This is just like patients — they feel the changes in fronts.

What studies show

Take your pick.

In a study published in 2019 involving 2,568 participants over a 15-month period, a group of British researchers found “significant” relationships between arthritis and how the humidity and barometric pressure were behaving. They cautioned, however, that those relationships were “modest.”

Similarly, a 2014 study of 222 Dutch osteoarthritis patients showed that barometric pressure and humidity had at least a small impact on pain.

Another analysis based on surveys of patient visits by more than 11 million Medicare recipients found no correlation with rainfall, however that study did not look at changing barometric readings and humidity.

Hollander and Climatron

Hollander’s Climatron experiments continued through the tumultuous ‘60s, and his own findings foreshadowed the conflicting research to come.

His mixed results notwithstanding, when it was over, Hollander again declared his work a success.

“Despite the innumerable frustrations and hours of wasted effort to achieve data reportable only in a ‘Journal of Negative Results,’” he wrote, that “‘old wives’ tale’ ... that arthritics can predict the weather has been statistically proved.”