Some support for patient claims seen in new study
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In a survey of 2,051 New Zealanders -- where gout is more common than anywhere else in the world -- 20.2% of individuals reported that tomatoes triggered their attacks, which was topped only by seafood (62.5%), alcohol (47.1%), and red meat (35.2%), according to Tony R. Merriman, PhD, of the University of Otago in Dunedin, and colleagues.
Moreover, a positive association with serum urate per serving of tomatoes per week was seen in data pooled from three cohorts with largely North American-European ancestry (beta 0.664, 95% CI 0.194 to 1.133, P=0.006), the researchers reported online in BMC Musculoskeletal Disorders.
But only one of these cohorts, the Atherosclerosis Risk in Communities, showed a significant association when analyzed individually (beta 0.907, 95% CI 0.264 to 1.550, P=0.006). It was not confirmed in the Cardiovascular Health Study (beta 0.216, 95% CI -1.341 to 1.772, P=0.786) or the Framingham Heart Study (beta 0.428, 95% CI -0.337 to 1.193, P=0.273).
"This is one in a long series of studies [from] researchers trying to confirm what gout patients tell them about food and drink as triggers of their gout flares," said N. Lawrence Edwards, MD, of the University of Florida in Gainesville, who was not involved in the research.
"However, the whole role of foods in the management of gout is more history than actual and practical," Edwards told MedPage Today.
"The problem is people trying to control their gout by diet alone. It doesn't work. People can't go on a restrictive enough diet so that their uric acid will be lowered to the point that they're not at risk of gout flares. What they need to do is go on pharmacologic therapy with the standard drugs -- allopurinol, febuxostat, probenecid -- to lower their uric acid. If they stay on that therapy, they aren't going to be susceptible to flares even if they have dietary indiscretions," said Edwards, who is chair of the Gout & Uric Acid Education Society.
Nonetheless, he said,"Gout has a long history of having triggers for disease. Any given individual with gout usually can come up with a list of things that they think will set their disease off," he said.
Case-control studies have linked alcohol and purine-rich foods as gout triggers, and these foods also have been shown to raise serum urate levels, "consistent with the hypothesis that they trigger acute gout attacks," according to Merriman and colleagues.
"People with gout also self-report food avoidances that have not been substantiated by the medical literature -- these avoidances include tomatoes and tomato products," Merriman's group wrote.
Therefore, to see if evidence backed this popular conception about tomatoes, he and his colleagues surveyed several ethnic groups in New Zealand, and found greater likelihood of self-reporting tomatoes as gout triggers compared with individuals of European ancestry:
- New Zealand Pacific Islanders, odds ratio 1.48 (95% CI 1.02 to 2.18, P=0.04)
- Ngati Porou Maori, OR 2.58 (95% CI 1.69 to 3.93, P=1 x 10-5)
- New Zealand Maori, OR 1.98 (95% CI 1.32 to 2.97, P=8.8 x 10-4)
"It is possible that self-recognition of attack triggers is a reflection of a greater community familiarity with gout due to a higher prevalence and longer disease history in Pacific Island and Maori populations," Merriman and colleagues noted.
"This is a very unusual population of patients who have truly terrible gout," Edwards commented.
"It's extremely prevalent, and it's harder to treat because of more consequences and comorbidities, so it's difficult to extrapolate these data to primarily European ancestry populations such as in the United States," he said.
"Whilst our data cannot support the claim that tomato consumption is a trigger of gout attacks, we provide support for the hypothesis that tomato consumption may trigger gout attacks through increasing serum urate," Merriman's group argued.
A potential mechanism for this effect is through the actions of glutamate, found in high levels in tomatoes, which can "stimulate or amplify the synthesis of urate by acting as a nitrogen donor in the purine synthesis pathway," they suggested.
"Further research into the relationship between gout (and onset of gout attacks) and tomatoes needs to be conducted," they concluded.
But the elevation in serum urate was small, according to Edwards, at 0.7 μmol/L -1 per one serving of tomatoes per week, compared with an increase of 2.3 μmol/L -1 per single serving of alcohol and 2.4 μmol/L -1 per serving of seafood per week.
"This increase could easily be overcome with uric acid lowering therapies," he said.
The authors reported no financial disclosures.
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