An investigation into the relationship between plain water intake and glycated Hb (HbA1c): a sex-stratified, cross-sectional analysis of the UK National Diet and Nutrition Survey (2008-2012)

Abstract

The aim of this study was to analyse the association between plain water intake and glycated Hb (HbA1c) in the National Diet and Nutrition Survey (2008-2012) rolling survey. These data included diet (4-d diaries) and HbA1c (fasted blood sample) measures of 456 men and 579 women aged 44 (sd 18) years with full information on covariates of interest (age, ethnicity, BMI, smoking status, education, other beverage intake, energy intake and fibre). Data were analysed using sex-stratified linear and logistic regressions modelling the associations of cups per d (240 ml) of plain water with HbA1c, and odds of HbA1c≥5·5 %, respectively. Substitution analyses modelled the replacement of sugar-sweetened beverages, fruit juice and artificially sweetened beverages with plain water. After adjustment, 1 cup/d of plain water was associated with a -0·04 % lower HbA1c (95 % CI -0·07, -0·02) in men. In logistic regression, men had a 22 % (95 % CI 10, 32 %) reduced odds of HbA1c≥5·5 %/cup per d of plain water. There was no evidence of an association with either HbA1c or odds of HbA1c≥5·5 % in women. None of the substitution models was associated with a change in odds of HbA1c≥5·5 %. Plain water intake was associated with lower HbA1c in men but not in women. Substituting water for specific beverages was not associated with a reduced odds of HbA1c≥5·5 %, suggesting that the addition of water is the more pertinent factor. Future trials should test whether the relationships between water intake and HbA1c is causal as this could be a cost-effective and simple health intervention.

Keywords: AVP arginine vasopressin; EER estimated energy requirements; EI energy intake; HbA1c glycated Hb; IQR interquartile range; NDNS National Diet and Nutrition Survey; PA physical activity; SSB sugar-sweetened beverages; T2D type 2 diabetes; Fluid balance; Glycated Hb; Hydration; Metabolism; Type 2 diabetes.

Fig. 1

Mechanisms potentially associating increased water intake with improved glycaemic control. Ingestion of plain water (PW) is a marker of a healthy lifestyle^{( 2 )}; part of this can manifest itself in consuming PW in place of unhealthy foods/beverages or by coincidental consumption of less unhealthy food. Further, PW intake is debatably linked to increased satiation^{( 3 )}, thus potentially reducing energy consumption. These factors contribute to improved glycaemia both indirectly (via weight stability) and directly (via fewer and/or lower blood glucose concentration spikes). Ingestion of PW also contributes to hydration. Improved hydration status reduces the secretion of arginine vasopressin (a blood pressure regulating hormone that plays an important role in glycaemic control)^{( 4 , 5 )}. Having an improved hydration status increases plasma volume, which could reduce the concentration of blood glucose^{( 6 )}. Finally, hydration status directly impacts osmolality, which in turn impacts arginine vasopressin secretion. Hydration also increases cell volume^{( 8 )}, which both impacts and is impacted by osmolality. Both these factors effect cellular glucose metabolism^{( 5 , 6 )}, resulting improved glycaemic control when euhydrated. Further, both dehydration^{( 6 )} and higher osmolality increase hepatic gluconeogenesis^{( 7 )}, which may negatively affect glycaemia. SSB, sugar-sweetened beverages.

Fig. 2

Flow chart of participant inclusion. NDNS, National Diet and Nutrition Survey; HbA1c, glycated Hb; PA, physical activity; T2D, type 2 diabetes.

Fig. 3

Percentage contribution of different sources of water by glycated Hb (HbA1c) categories (low cardiometabolic risk <5·5 %^{( – 28 )}; increased cardiometabolic risk 5·5–6·49 %^{( – 27 )}). Values are means, with their standard errors represented by vertical bars. Differences tested using Kruskal–Wallis test. * The difference in intakes between HbA1c categories is significant (P<0·05). ** The difference in intakes between HbA1c categories is significant (P=0·007). *** The difference in intakes between HbA1c categories is significant (P<0·001). , Men <5·5 % (n 221); , men ≥5·5 % (n 235); , women <5·5 % (n 295); , women ≥5·5 % (n 284). Excl., excluding.

Fig. 4

OR of glycated Hb (HbA1c) ≥5·5 % according to median plain water intake of each quintile of consumption in men. The likelihood ratio test suggested no evidence of deviation from linearity (P=0·600), calculated by comparing nested regression models.

Fig. 5

OR of glycated Hb (HbA1c) ≥5·5 % according to median plain water intake of each quintile in women. The likelihood ratio test suggested no evidence of deviation from linearity (P=0·451), calculated by comparing nested regression models.