The association of serum betaine concentrations with the risk of new-onset cancers: results from two independent nested case-control studies.

Evidence from epidemiologic studies on the association of circulating betaine levels with the incident risk of cancer has been inconsistent. We aimed to investigate the prospective association of serum betaine concentrations with the risk of cancer. We performed two, nested, case-control studies utilizing data from the "H-type Hypertension Prevention and Control Public Service Project" (HHPCP) and the China Stroke Primary Prevention Trial (CSPPT), with 2782 participants (1391 cancer cases and 1391 matched controls) in the discovery cohort, and 228 participants (114 cancer cases and 114 matched controls) in the validation cohort. Odds ratios (OR) of the association between betaine and cancer were calculated using conditional logistic regression models. There was an association between serum betaine as a continuous variable and total cancer (OR = 1.03, 95%CI = 0.99-1.07, p = 0.097). Among cancer subtypes, a positive association was found between serum betaine and the risk of lung cancer, and an inverse association was found with other cancers. Interestingly, a U-shaped association was observed between serum betaine and digestive cancers, with a turning point of 5.01 mmol/L for betaine (betaine < 5.01 mmol/L, OR = 0.82, 95%CI = 0.59-1.14, p = 0.228; betaine ≥ 5.01 mmol/L, OR = 1.08, 95%CI = 1.01-1.17, p = 0.036). In the validation cohort, a significant association between serum betaine as a continuous variable and total cancer (OR = 1.48, 95%CI = 1.06-2.05, P = 0.020) was also found. High serum betaine was associated with increased risk of total cancer and lung cancer, and a U-shaped association was found with the risk of digestive cancers, with a turning point at about 5.01 mmol/L.