The brief cognitive screening tests applied in this study included the Peruvian Spanish adaptation of the MMSE and the validated Spanish version of the IFS. The MMSE and IFS were selected given their utility among persons with educational levels of at least priong Spanish-speaking older adults (45). Moreover, the Peruvian Spanish version of the MMSE has https://www.datingranking.net/pl/cybermen-recenzja/ been found to be highly sensitive and specific when comparing dementia vs. MCI (sensitivity 87%, specificity 75%) among Peruvians living in Lima, Peru (46, 47). The MMSE is a brief cognitive screening tool that evaluates orientation (in time and space), immediate recall (or 3-word recall), attention and calculation, delayed recall, language (naming, repetition, reading, writing, performing verbal commands) and constructive praxis. We used the Peruvian version, modified from the Buenos Aires, Argentina version (32), and is administered in about 10 min, on average, and is based on a maximum score of 30 with a score <26 indicating cognitive impairment in a Peruvian population with >7 years of education (48) (Supplementary Material 1). The IFS is a screening test that uses eight sub-tests to assess executive function, with a maximum of 30 points, including motor programming (3 points), conflicting instructions (3 points), motor inhibitory control (3 points), backward digit span (6 points), verbal working memory (2 points), spatial working memory (4 points), abstraction capacity (3 points), verbal inhibitory control (6 points), where lower scores indicate poorer cognitive performance. The maximum score on the IFS is 30, and a score <23 indicates cognitive impairment in a Peruvian population with >10 years of education (33) (Supplementary Material 2). Functional assessment was completed using the PFAQ, which includes 11 questions assessing activities of daily living (ADLs), including an additional question on ability of the patient to take their own medications correctly. The maximum score on the PFAQ is 33, and a score >7 indicates functional impairment (49) (Supplementary Material 3).
Laboratory Analyses
A blood sample (3–5 ml of blood) was collected intravenously from the upper limb of the participants who were fasting for at least 12 h. Serum levels of folic acid < 3 ng/ dL and vitamin B12 <80 pg/mL were considered deficient. A low cut-off of < 80 pg/mL, previously utilized in other published studies (50, 51), was selected to ensure that any relationships detected between vitamin B12 levels and cognitive status were accurate. Of note, homocysteine and methylmalonic acid levels are unavailable in the laboratory where these laboratory results were obtained. Thyroid dysfunction was evaluated with measurements of levels of TSH, fT3, and fT4. According to verified laboratory reference ranges, the normal serum levels of TSH, fT3 and fT4 were 0.55–4.78 mIU/l, 3.50–6.50 pmol/l, and – pmol/l, respectively. Laboratory cut-offs for hypothyroidism were TSH level > 4.78 mIU/l, fT4 < or fT3 < 3.50 pmol/l, and hyperthyroidism were TSH level <0.55 mIU/l, fT4 > or fT3 > 6.50 pmol/l. Based on thyroid hormone levels, patients were classified into four categories: subclinical hyperthyroidism (low serum TSH with normal levels of fT3 and fT4), euthyroidism (TSH, fT3, and fT4 at normal values), subclinical hypothyroidism (elevated serum TSH with normal levels of fT3 and fT4) and clinical hypothyroidism (elevated serum TSH with low levels of fT3 and/or fT4), based on previously published criteria (52).
Statistical Investigation
Descriptive statistics were performed comparing demographics, brief cognitive screening and laboratory results of each cognitive group against one another (subjective cognitive decline-MCI, subjective cognitive decline-dementia, MCI-dementia) applying Chi-square (for categorical variables) or Analysis of One-Way Variance (ANOVA) for continuous variables. Bonferroni corrections were applied to adjust for these multiple comparisons. Participants were also divided into five quintiles based on lowest to highest TSH levels to allow for a logistic regression analysis to be performed using the fifth (or highest) quintile as the reference group. Logistic regression was used to assess the association of thyroid dysfunction with MCI and dementia (univariable logistic regression analyses were performed and multivariable logistic regression analyses adjusted for age, sex and BMI). Linear regression models comparing thyroid function, vitamin B12 and folate levels to MMSE and IFS scores, adjusted for age, sex, years of education and body mass index, were completed. For analyses in which vitamin B12 and folate levels were the dependent variables, conditional multiple logistic regression analyses were applied to obtain the odds ratios (OR) and p-value for any trends in the models. The first model was a crude model without variable adjustment. In the second model (adjusted model) the analyses were adjusted for regular exercise [utilized as a marker of cardiovascular health, a known risk factor for cognitive impairment (29)]. In the third model, where Vitamin B12 level was the dependent variable, any value >2,000 pg/mL was considered an outlier and excluded from the model. We also completed a sub-analysis of exploring the effect of folate and Vitamin B12 levels on AD. All calculated P-values were unpaired and two-tailed with differences considered significant at p < 0.05. Data were evaluated using 95% confidence intervals using STATA software (version 12.0).