Trial data showed an effect on cognitive decline from only 2 factors. Of these factors, the trial on cognitive training (176) concluded that domain-specific training was beneficial for maintaining cognition for the targeted domain. At 2 years after the intervention, the effect sizes for cognitive training, calculated as the difference in composite domain-specific mean performance of the groups divided by the intraparticipant SD, were 0.17 for memory (P < 0.001), 0.26 for reasoning (P < 0.001), and 0.87 for speed of processing (P < 0.001). These modest benefits remained at the 5-year follow-up. A single RCT (173) with 170 participants examined an intervention of physical exercise and reported that at 18 months (12 months after treatment), the treatment group showed a decrease of 0.73 point (CI, −1.27 to 0.03 point) on the 70-point Alzheimer's Disease Assessment Scale–Cognitive Subscale (lower scores indicate better performance). The control group showed a decrease of 0.04 point (CI, −0.46 to 0.88 point). The repeated measures analysis of covariance across the 6-, 12-, and 18-month follow-ups showed statistically significant improvement in the exercise group (P = 0.04). Observational studies for some factors, such as ω-3 fatty acids, the Mediterranean diet, vegetable intake, and some leisure activities, suggested a decreased risk for cognitive decline. However, RCT data on these factors are limited to absent and have no GRADE elements (such as a dose–response relationship) to strengthen the confidence in the association, so the quality of evidence for these factors is low.