Dietary iodine exposure and brain structures and cognition in older people. Exploratory analysis in the Lothian Birth Cohort 1936

Abstract

Background: Iodine deficiency is one of the three key micronutrient deficiencies highlighted as major public health issues by the World Health Organisation. Iodine deficiency is known to cause brain structural alterations likely to affect cognition. However, it is not known whether or how different (lifelong) levels of exposure to dietary iodine influences brain health and cognitive functions. Methods:From 1091 participants initially enrolled in The Lothian Birth Cohort Study 1936, we obtained whole diet data from 882. Three years later, from 866 participants (mean age 72 yrs, SD ±0.8), we obtained cognitive information and ventricular, hippocampal and normal and abnormal tissue volumes from brain structural magnetic resonance imaging scans (n=700). We studied the brain structure and cognitive abilities of iodine-rich food avoiders/low consumers versus those with a high intake in iodine-rich foods (namely dairy and fish). Results:We identified individuals (n=189) with contrasting diets, i) belonging to the lowest quintiles for dairy and fish consumption, ii) milk avoiders, iii) belonging to the middle quintiles for dairy and fish consumption, and iv) belonging to the middle quintiles for dairy and fish consumption. Iodine intake was secured mostly though the diet (n=10 supplement users) and was sufficient for most (75.1%, median 193 µg/day). In individuals from these groups, brain lateral ventricular volume was positively associated with fat, energy and protein intake. The associations between iodine intake and brain ventricular volume and between consumption of fish products (including fish cakes and fishcontaining pasties) and white matter hyperintensities (p=0.03) the latest being compounded by sodium, proteins and saturated fats, disappeared after type 1 error correction. Conclusion:In this large Scottish older cohort, the proportion of individuals reporting extreme (low vs. high)/medium iodine consumption is small. In these individuals, low iodine-rich food intake was associated with increased brain volume shrinkage, raising an important hypothesis worth being explored for designing appropriate guidelines.

Link Between Dietary Sodium Intake, Cognitive Function, and Dementia Risk in Middle-Aged and Older Adults: A Systematic Review

“…This review includes data from one clinical trial [27], six longitudinal cohort studies [28][29][30][31][32][33] (of which three studies only reported results of cross-sectional analyses [30,31,33]) and eight crosssectional studies [34][35][36][37][38][39][40][41] (Table 1). Six of the studies were conducted in the United States of America (USA) [27-29, 31, 32, 39], two studies were conducted in Australia [33,36], and one study each was conducted in Canada [30], Turkey [34], Korea [37], Poland [35], Scotland [38], Ireland [40], and China [41]. The only clinical trial included 160 participants who had subjective memory complaints, objective cognitive impairment (as assessed with the Montreal Cognitive Assessment [MoCA]), and at least one cardiovascular risk factor [27].…”

“…Follow-up time ranged from three to 36 years. The remaining eight [34][35][36][37][38][39][40][41] cross-sectional studies had sample sizes ranging from 44 [40] to 402 [35] participants with ages ranging from 50 to 85 years. Thirteen studies included both men and women, with two studies only including post-menopausal women [28,35].…”

“…Based on the NIHLB assessment tool four studies were rated as "good" [27][28][29][30], five were classified as "fair" [31][32][33][34]37], and six studies were rated as "poor" [35,36,[38][39][40][41]. The main issues across the studies included poorly defined study populations, non-reporting of participating rate, large proportion of missing data, and no adjustment for confounding factors.…”

“…Only one study used the Telephone Interview for Cognitive Status Modified (TICS-m) [41]. Three studies combined cognitive measurements to derive composite scores of cognitive performance [27,35,38]. Seven studies used more than one measure of cognition [27,28,31,[35][36][37][38].…”

“…In contrast, women who reported they "sometimes" add salt after cooking had better cognitive function than women who reported "never". Two studies [35,38] using a composite of tests to derive a global cognition score both reported no association between sodium intake and cognitive function (see Table 2).…”