The reviewed study is interesting, not only because it investigated how very little sleep may affect your memory, but also how a lot of sleep can influence it(Devore EE,et al. 2014).
The participants were 15,385 female nurses and 4 repeated assessments were performed over 6 years. Women sleeping 5 hours or less had worse cognition than those who were sleeping 7 hours, and so did the women who slept more than 9 hours. Women whose sleep duration changed by 2 hours or more over time also had worse cognitive function than the women with no change in sleep duration. It was concluded that extreme sleep duration at midlife and later life, and also extreme changes in sleep duration are associated with poor cognition in older women. The message is that it is not only important to sleep well in your older years, but also how you sleep earlier in life may affect your memory when you get older.
Devore EE1, Grodstein F, Duffy JF, Stampfer MJ, Czeisler CA, Schernhammer ES. Sleep duration in midlife and later life in relation to cognition. J Am Geriatr Soc. 2014 Jun;62(6):1073-81. doi: 10.1111/jgs.12790. Epub 2014 May 1.