Abstract of online articleSodium intake and physical activity impact cognitive maintenance in older adults: the NuAge Study
Introduction
Sodium intake is of great interest due to its association with blood pressure regulation and heart disease. Heart disease is a major cause of mortality and disability, especially in individuals 60 years and older (Mathers and Loncar, 2006, Woloshin et al., 2008). Animal and human studies have shown that high sodium intake is associated with increased blood pressure and cardiovascular disease (Cook, 2008, Denton et al., 1995, Stamler, 1997). Based on robust findings, national and international groups, including the World Health Organization (WHO), have set out to promote reductions in sodium intake at the population level to reduce the incidence of cardiovascular disease (Institute of Medicine, 2010; Minister of Health, 2007; WHO, 2007).
While lowering sodium consumption is associated with reduced blood pressure and risk of heart disease (Cutler, 1991), less is known about the effect of sodium intake on cognitive function. With population aging, there is both a rise in cardiovascular events and a projected expansion of dementia cases in late life (Brookmeyer et al., 1998). Furthermore, risk factors for cardiovascular disease, including hypertension, are also common risk factors for dementia (Grodstein, 2007, Purnell et al., 2009). Thus, it may be postulated that sodium intake not only impacts heart health, but brain health as well.
Hypertension at midlife is reportedly associated with worse cognitive function in late life (Kloppenborg et al., 2008). Studies show that hypertension may mediate adverse effects on brain function through a number of mechanisms, including altered cerebral endothelium, vascular remodeling, impaired cerebral autoregulation, cerebral microbleeds, white matter hyperintensities (WMH), unrecognized lacunar infarcts, and Alzheimer-like changes such as amyloid angiopathy and cerebral atrophy (Manolio et al., 2003). However, according to a Cochrane systematic review, there is no convincing evidence that lowering blood pressure in older adults prevents the development of cognitive impairment or dementia (McGuinness et al., 2009).
Although there is a paucity of research that examines the impact of sodium intake on brain health, research has increasingly examined the link between diet and cognitive function in late life. Research shows that adherence to a Mediterranean diet, which is high in fruits and vegetables, reduces the rate of cognitive decline with age (Tangney et al., 2011). Furthermore, dietary fat intake has been found to associate with cognitive function. Specifically, fatty fish and omega-3 fatty acids are associated with good cognitive health, whereas saturated fat intake is associated with increased risk of impaired cognitive function (Kalmijn et al., 1997, Kalmijn et al., 2004). Specific nutrients, including vitamins D, E, and B-complex, have been examined in relation to cognitive function in late life (Annweiler et al., 2010, Morris et al., 2007, Usoro and Mousa, 2010). In a small cross-sectional study that assessed the relationship between nutrient intake and cognitive performance in people at risk of dementia, it was found that cholesterol and sodium intakes differentiated middle-aged adults who scored within the normal range on a test of global cognitive function compared with those who scored below the normal cutoff (Salerno-Kennedy and Cashman, 2007).
In addition to reductions in sodium intake, research has shown that physical activity may improve both cardiovascular and cognitive health (Brown et al., 2010, Eskes et al., 2010, Jedrziewski et al., 2010, Kelley and Kelley, 2008, Kramer et al., 2006, Maiorana et al., 2011). Furthermore, an additive effect of reduction in sodium intake and physical exercise has been reported in hypertensive adults. In a randomized controlled trial that assessed the effect of a reduced sodium diet (Dietary Approaches to Stop Hypertension; DASH) and exercise program on neurocognitive function in sedentary, overweight hypertensive adults, it was found that individuals in the combined DASH plus exercise group showed the most pronounced improvement in cognitive function, compared with individuals in the DASH diet alone. It was also reported that the greatest neurocognitive improvement was observed in those with the highest level of systolic blood pressure (Smith et al., 2010).
The present study assessed the association between sodium intake and global cognitive function over 3 years of follow-up in older adults. Specifically, the present study examined 3 questions: (1) is there a direct association between sodium intake and cognitive function?; (2) does hypertension moderate the association between sodium intake and cognitive function?; and (3) is there an additive impact of sodium intake and physical activity on cognitive function?. To this end, it is hypothesized that higher sodium intake will associate with lower cognitive function over time and this relationship will be moderated by the presence of hypertension. Further, based on the DASH report (Smith et al., 2010), it is hypothesized that low sodium intake and high physical activity will impose an additive positive effect on cognitive function in older adults.
Section snippets
Study Population
We examined a subgroup of participants from the Québec Longitudinal Study on Nutrition and Successful Aging (NuAge Study), a 5-year prospective study of 1793 cognitively intact and functionally independent elders aged 67–84 years upon recruitment, described in more detail elsewhere (Bouchard et al., 2007, Gaudreau et al., 2007). Participants in the original cohort were randomly selected from the Québec Medicare database and were stratified by age and sex. They were tested annually at the
Baseline characteristics
Among 1262 participants, 420 fell into the low sodium intake tertile group (median [M] = 1791 mg/day, standard error [SE] = 15), 421 fell into the mid tertile group (M = 2648 mg/day, SE = 11) and 421 fell into the high tertile group (M = 3919 mg/day, SE = 36) (for median and range values, see Table 1). Tertile groups differed on total energy, cholesterol, and calcium intake, and total C-HEI score (p < 0.001). Baseline characteristics including sex, waist circumference, physical activity, and
Discussion
Worldwide sodium reduction strategies are being recommended with a focus on reducing heart disease. It is estimated that a reduction in sodium intake may result in major annual savings in medical care costs and physician visits related to hypertension (Joffres et al., 2007). Sodium intake reduction has been reported to be especially beneficial in older populations (Alam and Johnson, 1999, Cappuccio et al., 1997). This study suggests that sodium intake reduction, especially in low physical
Disclosure statement
None of the authors report any conflict of interest.
The protocol was approved by the REB of the institutions involved in the study: Institut Universitaire de Gériatrie de Montréal and the Institut Universitaire de Gériatrie de Sherbrooke. All participants signed an informed consent approved by the ethics committee at each institution.
Acknowledgements
We thank other members of the NuAge and NutCog groups for enabling this study through the development of the infrastructure and providing the essential databases. We also thank Katherine Gray-Donald and Pierrette Gaudreau for their insightful comments on the manuscript.
The NuAge Study is supported by CIHR MOP-62842. NutCog is supported by CIHR MOP-81217. A.J.F. is supported by a Canadian Institute of Health Research Fellowship.
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