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Background: To investigate the relationship between dietary intake of niacin (water‐soluble form of vitamin B3) and retinal nerve fibre layer (RNFL) thickness in healthy eyes. Methods: This cross‐sectional study examined the association between daily niacin intake and RNFL thickness in three large population‐based cohorts with varied age differences. RNFL thickness was extracted from optical coherence tomography data; energy‐adjusted niacin intake was estimated from food frequency questionnaires. Linear mixed‐effects models were utilised to examine the association between RNFL thickness and energy‐adjusted niacin intake. Three separate analyses were conducted, with niacin treated as a continuous, a categorical (quartiles) or a dichotomous (above/below Australian recommended daily intake) variable. Results: In total, 4937 subjects were included in the study [Raine Study Gen2, n = 1204, median age 20; Busselton Healthy Ageing Study (BHAS), n = 1791, median age 64; TwinsUK, n = 1942, median age 64). When analysed as a continuous variable, there was no association between RNFL thickness and niacin intake in any of the three cohorts (95% CI β: Raine Study Gen 2, −0.174 to 0.074; BHAS, −0.066 to 0.078; TwinsUK −0.435 to 0.350). Similar findings were observed with quartiles of niacin intake and for niacin intakes above or below Australian recommended daily intake levels in all three cohorts. Conclusions: Dietary intake of niacin from a standard diet does not appear to be associated with age‐related RNFL thinning in healthy eyes. Supraphysiological doses of niacin may be required for therapeutic effect in the retina. [ABSTRACT FROM AUTHOR]

Background: The Dietary Approaches to Stop Hypertension (DASH) diet is beneficial in reducing blood pressure; however, this may be a consequence of concurrent weight reduction. In the present study, we investigated whether body mass index (BMI) mediates the association between the DASH diet and hypertension and investigate common metabolic pathways. Methods: We included 2424 females from the cross‐sectional TwinsUK cohort, with blood pressure, BMI and dietary intake measured within 1.01 (SD = 0.68) years and serum metabolomics profiling (591 metabolites). We constructed a mediation model to test the mediation effects of BMI on the total effect of the DASH diet on hypertension. To identify a metabolite panel associated with the DASH diet and BMI, we built random forest models for each trait, and selected the common metabolic contributors using five‐fold cross‐validation error. Results: We found that BMI fully mediates the association between the DASH diet and hypertension, explaining 39.1% of the variance in hypertension. We then identified a panel of six common metabolites predicting both the DASH diet and BMI with opposing effects. Interestingly, at the univariate level, the metabolites were also associated with hypertension in the same direction as BMI. The strongest feature, 1‐nonadecanoyl‐GPC (19:0), was positively associated with the DASH diet (β [SE] = 0.65 [0.12]) and negatively with BMI (β [SE] = −1.34 [0.12]) and hypertension (odds ratio = 0.71, 95% confidence interval = 0.6–0.84). Conclusions: We highlight the role of BMI in the mechanisms by which the DASH diet influences hypertension and also highlight common metabolic pathways. Further studies should investigate the underlying molecular mechanisms to increase our understanding of the beneficial ways of treating hypertension. Key points: Adherence to the DASH diet can reduce blood pressure; however, this may be a consequence of concurrent weight reduction.In a large sample of 2424 females from TwinsUK, we report that BMI fully mediates the association between the DASH diet and hypertension, explaining 39.1% of the variance in hypertension.We also identify a panel of six common metabolites predicting both the DASH diet and BMI with opposing effects, highlighting common metabolic pathways.Further studies should investigate the underlying molecular mechanisms to increase our understanding of the beneficial ways of treating hypertension. [ABSTRACT FROM AUTHOR]