The thesis reports on 6 studies (2 of which were part of a multi-centre trial) examining hydration and fluid balance. The first study described in this thesis investigated the impact of hydration status on Dual energy x-ray absorptiometry (DXA) and other methods that are popular tools to determine body composition in athletes. We observed that it is important to ensure a euhydration when assessing body composition, particularly when considering changes associated with nutritional or exercise interventions. The second and third studies reported identified beverages that promote longer term fluid retention and maintenance of fluid balance in adults. We investigated the effects of 13 different commonly consumed drinks on urine output and fluid balance when ingested in a euhydrated state, with a view to establishing a beverage hydration index (BHI), i.e., the volume of urine produced after drinking expressed relative to a standard treatment (still water) for each beverage. The beverages with the highest BHI were oral rehydration solution, full fat milk and skimmed milk. BHI may be a useful measure to identify the short term hydration potential of different beverages when ingested in a euhydrated state. The fourth study aimed to systematically examine the influence of carbohydrate, sodium and caffeine content of beverages on the BHI. The BHI was greater in beverages with higher carbohydrate or higher sodium content, but not influenced by caffeine. The carbohydrate content of beverages has no effect on BHI at concentration up to 10% carbohydrate. Sodium content of beverages in concentrations of 27mmol/L and higher can improve the hydration potential of beverages. Caffeine doses in beverages up to 400mg/L do not have an impact upon diuresis when ingested in a euhydrated state. The fifth study compared net fluid balance (NFB) responses to the ingestion of commonly consumed drinks in young and older men. We observed that in young adults milk helps to maintain positive net fluid balance for longer than other drinks. In older adults this effect of milk is not observed despite similar net electrolyte balance responses. Future work should more fully explore these potential differences in fluid balance responses to drink ingestion between young and older adults. The final study investigated the hydration habits of Scottish young and older adults (+50 years old), identifying their fluid choices, volume, and preferences in relation to time of day. The results showed that 26.1% of the young females, 30.3% of the young males, 25.8% of the older females and 50.4% of the older males did not meet the European (EU) Food Safety Authority (EFSA) fluid intake recommendations. We also observed that the difference between those who met and those who did not meet the EFSA adequate intake could be attributed to differences in water ingestion, mainly during the mid-morning (after breakfast until 11 am) and during the early-afternoon (after lunch time up to 5 pm). It was concluded that these moments might be key when implementing interventions to improve hydration status especially in the older population.

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Introduction: Les personnes vivant avec le VIH (PVVIH) présentent des risques accrus d’ostéoporose et de lipodystrophie. Peu d’études se sont penchées sur l’association entre les déterminants du style de vie, le risque d’ostéoporose et le risque de lipodystrophie chez les PVVIH. Objectifs: L’objectif primaire était d’évaluer l’association entre l’ostéoporose, la lipodystrophie ainsi que différents déterminants du style de vie chez les PVVIH. Méthodologie: Tous les participants de la Cohorte canadienne VIH et vieillissement (CCVV) avec des données sur la densité minérale osseuse (DMO), mesurée par absortiométrie biphotonique à rayons X (DXA), ont été inclus dans cette étude transversale. Les déterminants du style de vie d’intérêt étaient : le revenu annuel, le niveau d’éducation, l’exercice physique ainsi que les consommations d’alcool, de tabac et de drogues illicites. Les covariables mesurées incluaient l’historique complet de la médication antirétrovirale, les comorbidités, les co-infections, la charge virale, le compte de CD4+ au recrutement et le compte de CD4+ nadir. L’ostéoporose a été définie par un score T de -2.5 ou moins. La lipodystrophie, évaluée par la composition corporelle via DXA, a été définie par un fat mass ratio (rapport des pourcentages de gras entre le tronc et les membres inférieurs) supérieur à 1.33 pour les femmes et 1.96 pour les hommes. Les rapports des cotes et les intervalles de confiance à 95% (IC95%) au recrutement ont été estimés en utilisant des régressions logistiques multivariées. Résultats: Nous avons inclus 547 PVVIH (âge médian 55 ans, 88% d’hommes) et 97 contrôles séronégatifs au VIH (âge médian 54 ans, 54% d’hommes). L’ostéoporose était présente chez 13% des PVVIH et 6% des contrôles (OR 2.21, IC 95% [0.96 – 6.06]). La lipodystrophie était présente chez 138 (28.3%, IC 95% 24.3 – 32.3%) des 487 PVVIH avec des données sur la disposition du gras corporel. Aucun des déterminants du style de vie était associé à l’ostéoporose ou à la lipodystrophie. Par contre, les covariables associées à un risque accru d’ostéoporose étaient l’âge avancé, un indice de masse corporelle (IMC) réduit et la co-infection à l’hépatite C. Les covariables associées au risque accru de lipodystrophie étaient l’âge avancé, l’hypertension, l’exposition prolongée aux antirétroviraux, ainsi que les expositions prolongées aux inhibiteurs nucléosidiques de la transcriptase inverse (INTI) et aux inhibiteurs de l’intégrase (INI). Conclusion: Aucune association n’a été décelée entre les déterminants du style de vie étudiés et l’ostéoporose ou la lipodystrophie. / Background: As a consequence of ART, people living with HIV (PLWH) are at higher risk for osteoporosis and lipodystrophy. However, the risk may also be influenced by lifestyle factors, but few studies have explored the association between modifiable lifestyle factors and the risk of osteoporosis or lipodystrophy in the PLWH population. Objectives: Our primary objective was to evaluate the lifestyle factors in relation to the risks of osteoporosis and lipodystrophy in a PLWH-based cohort. Methods: We conducted a cross-sectional analysis of data from the Canadian HIV and Aging Cohort Study (CHACS). We included all participants with available bone mineral density T-scores, which were measured by dual-energy X-ray absorptiometry (DXA) scans. Lifestyle risk factors of interest included annual income, education level, alcohol intake, tobacco use, illicit drug use and physical exercise. Other covariates considered were full antiretroviral medication history, medical comorbidities, coinfections, viral load, nadir CD4+ and current CD4+ count. Osteoporosis was defined by a T-score of -2.5 or lower at any of the measured sites. Lipodystrophy was assessed on whole body DXA and defined as a fat mass ratio (the ratio between trunk and lower limbs fat mass) greater than 1.33 for women and 1.96 for men. Baseline prevalence odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated by multivariate logistic regressions. Results: We included 547 PLWH (median age 55 years, 88% males) and 97 HIV-uninfected controls (median age 57 years, 64% males). Osteoporosis was present in 13.0% of PLWH (95% CI 10.2 – 15.8%) and 6% of controls (95% CI 1.4 – 11.0%); the OR of osteoporosis for HIV seropositivity was 2.21 (95% CI [0.96 – 6.06]). Lipodystrophy was found in 138 (28.3%, 95% CI 24.3 – 32.3%) of the 487 PLWH for which a fat mass ratio (FMR) was available. None of the lifestyle factors of interest were associated with osteoporosis or lipodystrophy. However, covariates associated with an increased risk of osteoporosis were increasing age, lower body mass index (BMI) and hepatitis C coinfection. Covariates associated with an increased risk of lipodystrophy were older age, hypertension, longer antiretroviral duration, and longer exposure to nucleoside reverse transcriptase inhibitors (NRTIs) and integrase strand inhibitors (INSTIs). Conclusion: No association was found between any of the lifestyle factors of interest and osteoporosis or lipodystrophy.