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Introduction
Alzheimer disease (AD), the most common form of dementia, affects more than 5 million Americans, placing a tremendous strain on our healthcare system [1]. Due to the severity of the problem, research on potentially modifiable risk factors has increased, including the investigation of the role of diet in the onset and prevention of AD [2]. Recent guidelines [3] for AD prevention addressed such dietary factors as saturated fat and trans fat intake, vitamins (especially vitamins E and B12), and the intake of vegetables, legumes, and fruits. Higher levels of the minerals iron and copper were identified as being related to increased risk for AD but the role of other minerals (such as potassium) in cognitive decline was not addressed. The literature on minerals and cognitive impairment associated with dementia is limited. Ozawa et al. [4] studied a community-based Japanese cohort investigating the relationship of self-reported dietary intake of potassium, calcium, and magnesium and the occurrence of dementia over a 17-year period. They found that increased dietary intake of potassium, calcium, and magnesium reduced the risk of all-cause dementia especially vascular dementia. The risk of AD tended to decrease with higher reported dietary mineral intake, but there was no significant linear progression. In another study assessing potassium and cognitive abilities, Cisternas et al. [5] used an animal model of AD to find that increased potassium yielded reduced markers of oxidative stress and inflammation and improved cognition. Additionally, potassium was related to a change in the aggregation pattern of Aβ peptide and a reduction in tau phosphorylation. Mielke et al. [6] investigated the relationship between potassium and Aβ42, a cerebrospinal fluid marker that was decreased in AD in a prospective population-based study of 1,622 women over a 24-year period. An association was found between higher serum potassium and higher levels of Aβ42 in 1968 and 1974, but not in later years, suggesting that potassium is associated with dementia in midlife but not late life. Similar patterns have been found in studies of other vascular risks, such as hypertension [7], high cholesterol [8], and obesity [9]. Despite the growing literature on the relationship of potassium to AD, there has been little research on the relationship of potassium to mild cognitive impairment (MCI). MCI is defined...