Salicylic acid in the serum of subjects not taking aspirin. Comparison of salicylic acid concentrations in the serum of vegetarians, non-vegetarians, and patients taking low dose aspirin

C J Blacklock¹, J R Lawrence², D Wiles¹, E A Malcolm², I H Gibson³, C J Kelly², J R Paterson¹

¹ Area Biochemistry Department, Dumfries and Galloway Royal Infirmary, Bankend Road, Dumfries, Scotland, DG1 4AP, UK
² Department of Medicine, Dumfries and Galloway Royal Infirmary
³ Department of Pathology, Dumfries and Galloway Royal Infirmary

Correspondence to:
Dr Paterson J.Paterson{at}dgri.scot.nhs.uk

Aims—To determine serum salicylic acid concentrations in non-vegetarians and vegetarians not taking salicylate drugs, and to compare these concentrations with those found in patients taking aspirin, 75 mg daily.

Methods—Serum samples were obtained from vegetarians (n = 37) and non-vegetarians (n = 39) not taking salicylate drugs. Non-vegetarians and vegetarians were recruited from the community and from a Buddhist monastery, respectively, in Dumfries and Galloway, Scotland. Patients (n = 14) taking aspirin (75 mg daily) were recruited from the Dumfries diabetic clinic. Serum salicylic acid concentrations were determined using a high performance liquid chromatography method with electrochemical detection.

Results—Salicylic acid was detected in every serum sample analysed. Higher serum concentrations of salicylic acid were found in vegetarians than non-vegetarians: median concentrations of 0.11 (range, 0.04–2.47) µmol/litre and 0.07 (range, 0.02–0.20) µmol/litre, respectively; the median of the difference was 0.05 µmol/litre (95% confidence interval for difference, 0.03 to 0.08; p < 0.0001). The median serum concentration of salicylic acid in patients taking aspirin (75 mg daily) was 10.03 (range, 0.23–25.40) µmol/litre, which was significantly higher than that found in non-vegetarians and vegetarians. There was overlap in serum salicylic acid concentrations between the vegetarians and patients taking aspirin.

Conclusions—Salicylic acid, a non-steroidal anti-inflammatory drug, is present in fruits and vegetables and is found in higher concentrations in vegetarians than non-vegetarians. This suggests that a diet rich in fruits and vegetables contributes to the presence of salicylic acid in vivo. There is overlap between the serum concentrations of salicylic acid in vegetarians and patients taking aspirin, 75 mg daily. These findings may explain, in part, the health promoting effects of dietary fruits and vegetables.

Key Words: salicylic acid • salicylates • diet • low dose aspirin

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