Risk of hypothyroidism in meat-eaters, fish-eaters, and vegetarians: A population-based prospective study

Abstract

BackgroundGlobally, plant-based diets are gaining in popularity. Whilst their cardiometabolic benefits are well-documented, there is a lack of studies examining the associations between plant-based diets and risk of hypothyroidism.MethodsWe analysed data from the UK Biobank cohort. Multivariable Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs) for incident hypothyroidism across vegans, vegetarians, pescatarians, poultry eaters, low meat eaters, and high meat eaters aged 40-69 years. Ancillary to this, we carried out logistic regression analysess to evaluate associations between the diet groups and prevalent hypothyroidism (according to International Classification of Diseases (ICD) codes at baseline.ResultsWe included 494,437 individuals from the UK Biobank, of which 231,906 followed a high-meat, 236,510 a low-meat, 5,662 a poultry-based, 11,286 a pescatarian, 8,654 a vegetarian, and 419 a vegan diet. During a median (SD) follow-up of 12.7 (± 3.2) years, 24,240 participants developed hypothyroidism. In multivariable Cox regression models without adjustment for body mass index (BMI), none of the diets were significantly associated with the risk of hypothyroidism. However, there was a tendency for a higher risk of hypothyroidism among vegetarians compared to people following a high-meat diet (HR: 1.08, 95% CI: 0.98 - 1.19). After controlling for BMI the association for vegetarians (HR = 1.18, 95% CI 1.07 – 1.30) became stronger and statistically significant. Furthermore, we observed a positive association between a vegetarian (OR: 1.37, 95% CI: 1.14 - 1.63) and a poultry diet (OR: 1.35, 95% CI: 1.10 1.63) with hypothyroidism prevalence.ConclusionIn the present study, we found a moderately higher risk of hypothyroidism among vegetarians, after controlling for BMI, a potential collider. This slightly higher risk of hypothyroidism among vegetarians, requires further investigation, taking iodine status and thyroid hormone levels into account.