Two randomized controlled trials have been published in the recent past, one last year, and the other just a few months back, that look at the effectiveness of curcumin as a treatment for knee pain, and more specifically for knee pain induced by osteoarthritis.
A systematic review published in Canadian Family Physician in March found that the medications most commonly prescribed at present are often useless. Acetaminophen (paracetamol), the most common medication prescribed to patients with pain due to osteoarthritis, is completely ineffective (no better than placebo). Opioids (for example morphine, oxycontin) are also of extremely limited value, and show no benefit whatsoever after four weeks, so they don’t work at all as a treatment for chronic pain.
The most effective treatments at present are cortisone injections in to the affected joint, oral NSAIDS (non-steroidal anti-inflammatory drugs – for example aspirin and ibuprofen), and duloxetine (a drug mostly used to treat depression, that works by increasing the levels of signaling molecules serotonin and noradrenalin in the junctions between neurons). But none of these is particularly effective. Only one in five to six people sees any benefit when compared with placebo.
Even knee replacement surgery is of questionable value. A study published in the British Medical Journal in 2017 found that knee replacement surgery only provides marginal benefit to quality of life. The authors of the study therefore only recommended it for the most severely afflicted people, when nothing else helps.
As I think is clear by now, there are no good treatments available at present for chronic knee pain due to osteoarthritis. Considering how common the condition is, that is a big problem. Any treatment that could be shown to be cheap, safe, and even only moderately effective, would literally be worth its weight in gold.
That is why I think the two recent studies of curcumin are so interesting. Curcumin is a molecule found in turmeric, a plant that grows in Asia, and that has been used in Asian cooking and folk medicine for at least a few thousand years. It is the curcumin that gives turmeric its distinctive yellow color.
The first study we’re going to talk about was published in Arthritis Research and Therapy in July 2019. It was a double-blind randomized controlled trial (yes, I agree, those are the five most beautiful words in the English language – at least when put in that order). The study was funded by Tilman SA, a company that (surprise, surprise) sells turmeric supplements, and it was carried out in Belgium.
In order to be included in the study, participants had to have had knee pain due to osteoarthritis for at least three months, with a self-estimated pain level of at least 40 on a 100-point scale (where zero is no pain and 100 is the worst pain imaginable). They also had to already be taking paracetamol and/or an oral NSAID for their pain (the researchers wanted to see if curcumin could provide effective pain relief on top of what the patients were already getting from the standard recommended therapy).
Participants were randomly assigned to one of three groups. A low dose curcumin group (47 participants) took 94 mg of curcumin twice per day (total daily dose 188 mg per day), while a high dose group (49 participants) took 141 mg of curcumin twice per day (total daily dose 282 mg). The third group was the placebo group (45 participants), which received identical placebo capsules twice per day.
The average age of the participants was 62 years, and they had on average been suffering from osteoarthritic knee pain for seven years. Patients were generally overweight (average BMI 29), and they had a self-estimated pain level of on average 63 out of 100 in both intervention groups, and 60 out of 100 in the placebo group.
Ok, let’s get to the results. Both the high dose and low dose curcumin group showed statistically significant reductions in knee pain when compared with placebo, at both the one month and three month marks. In the two curcumin groups, self-estimated pain dropped from 63 to 46 at the one month mark, and further to 38 at the three month mark (25 point reduction overall). In the placebo group, pain dropped from 60 to 55 at the one month mark, and further to 49 at the three month mark (11 point overall reduction). There was no statistically significant difference between high dose and low dose curcumin in terms of pain reduction.
Adverse events were most common in the high dose curcumin group (37%), less common in the low dose curcumin group (21%), and least common in the placebo group (13%). The difference between the high dose group and the placebo group was statistically significant, while the difference between the low dose group and the placebo group wasn’t. The most common adverse events were abdominal discomfort and diarrhea.
What can we conclude? This study suggests that curcumin is an effective treatment for knee pain due to osteoarthritis. High dose curcumin (282 mg per day) does not seem to be more effective than low dose (188 mg per day) at reducing pain, but does seem to cause more stomach upset, so it’s probably better to stick with the lower dose.
The study was financed by a company with a financial interest in selling curcumin supplements. This should of course make us a little bit wary of the results, and the study was quite small. However, the methodology was sound.
Next up we have a study that was published in September 2020 in The Annals of Internal Medicine. Like the previous study, this one was double-blind, randomized and placebo controlled. And like the previous study, it was funded by a company that sells curcumin supplements (a company with the apt name “Natural Remedies”), along with the University of Tasmania. The research was carried out in Australia.
In order to be included in the study, patients had to be older than 40 years of age, have a self-estimated pain of at least 40 on a 100 point scale, have a confirmed diagnosis of knee osteoarthritis, and have signs of inflammation in the knee joint when examined with ultrasound.
70 participants were included in the study, and were randomized to receive either 500 mg of curcumin twice per day (total daily dose 1,000 mg) or placebo twice per day. They were followed for twelve weeks and asked to estimate knee pain at multiple time points. Note that the dose in this study was more than three times higher than the highest dose used in the previous study.
The participants were 62 years old on average, and had an average BMI of 30 (marginally obese). The average self-estimated pain level at the beginning of the study was 56 out of 100 in the treatment group and 55 in the placebo group.
So, what were the results?
At the twelve week mark, knee pain had decreased from 56 to 32 in the curcumin group (24 point reduction), and from 55 to 40 in the placebo group (15 point reduction). The difference was statistically significant. In fact, patients in the treatment group showed a greater reduction in knee pain that patients in the placebo group at every time point measured (one week, four weeks, eight weeks, and twelve weeks).
39% of participants in the curcumin group had at least one adverse event over the course of the twelve weeks, compared with 53% in the placebo group. The difference was not statistically significant. This is a bit odd, and quite different from the previous study. Even though the dose of curcumin given was much higher than in the previous study, there was no statistically significant difference in adverse events between the groups.
This shows the importance of doing multiple studies on a subject before considering a matter settled. The results of the two studies together mean that it’s impossible to say whether curcumin causes more adverse events than placebo. More studies will need to be done before the matter can be considered settled.
What can we conclude overall from these two studies?
Curcumin does seem to be an effective and safe treatment for knee pain due to osteoarthritis, although new, bigger studies should be done to confirm the results from these two trials. Ideally, companies that sell supplements should have no role in funding those studies.
I find it interesting that the effect size was very similar in the two trials. In both studies, the placebo group experienced roughly a 20-25% reduction in pain, while the curcumin group experienced roughly a 40% reduction in pain. That is pretty much equivalent to the effect seen with NSAID’s. Overall, giving a higher dose did not seem to result in less pain, so it seems like the lowest dose given in the first study (188 mg per day) is enough to achieve maximal benefit in terms of pain reduction.
Considering that the current first-line treatments for pain due to osteoarthritis are either completely ineffective (acetaminophen) or connected with significant dangers when used long term, especially in elderly people (NSAID’s), I think it is reasonable to try curcumin if you have knee pain, and see what happens.
You might also be interested in my article about whether vitamin C is effective against the common cold or my article about whether vitamin D can be used to cure covid-19.