Following ingestion of a variety of drinks, subsequent urine excretion in humans shows large variability.1 The reasons for this are currently unknown. Aldosterone, the end product of the renin angiotensin aldosterone system (RAAS), increases sodium and water re-absorption in the kidney. Circulating concentrations of angiotensin-converting enzyme (ACE), a key component of the RAAS, are affected by a polymorphism in the ACE gene involving the deletion (D) or insertion (I) of a 287 base pair sequence, with DD genotypes resulting in higher circulating concentrations of ACE.2 Following ethical approval, 29 healthy Caucasian males participated in this investigation. Participants arrived at the laboratory hydrated after an overnight fast. Following arrival, participants' height and body mass were measured before a 15-min supine rest period. Total body water was measured before a fingerprick blood sample was obtained in order to determine ACE genotype. Participants then provided a urine sample before ingesting 600 ml of a commercially available sports drink over a period of 5 min. A further urine sample was obtained 60 min later. Urine samples were analysed for osmolality and sodium concentration. The I allele (corresponding to either ID or II genotypes) was found in 12 participants and 17 participants were found not to have the I allele (corresponding to a DD genotype). Baseline characteristics of the two groups were the same (p>0.05) with the exception of height. Pre-ingestion urine volume and osmolality were the same for both groups (p>0.05). Following ingestion of the drink, urine volume amounted to 420±258 ml for those with the I allele and 337±160 ml for those without the I allele (p=0.293). This pilot study found that, although not statistically significant, participants with the I allele had a lower urine volume than those without the I allele, amounting to a reduction of approximately 80 ml (19%). Further investigations are now warranted in a larger participant cohort to determine whether the ACE genotype is statistically associated with fluid retention after ingestion.
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