There is now evidence to suggest that there may be an interaction between B vitamins and n -3 PUFA, with suggestions that increasing intake of both nutrients simultaneously may benefit cognition in older adults. The aim of this systematic review was to investigate whether supplementation with a combination of n -3 PUFA and B vitamins can prevent cognitive decline in older adults. Randomised controlled trials conducted in older adults that measured cognitive function were retrieved. The included trials provided a combination of n -3 PUFA and B vitamins alone, or in combination with other nutrients. Trials that provided n -3 PUFA alone and also measured B vitamin status or provided B vitamin supplementation alone and measured n -3 PUFA status were also included. The databases searched were The Cochrane Library, EMBASE, CINAHL, Scopus and MEDLINE. A total of 14 papers were included in the analysis (n 4913; age: 60–70 years; follow-up 24 weeks to 4 years). The meta-analysis results found a significant benefit of nutrient formulas, which included both n -3 PUFA and B vitamins alongside other nutrients, v. placebo on global cognition assessed using composite scores from a neuropsychological test battery (G = 0·23, P = 0·002), global cognition using single measures of cognition (G = 0·28, P = 0·004) and episodic memory (G = 0·32, P = 0·001). The results indicate that providing a combination of n -3 PUFA and B vitamins as part of a multi-nutrient formula benefits cognition in older adults v. a placebo, and the potential for an interaction between these key nutrients should be considered in future experimental work. [ABSTRACT FROM AUTHOR]