Taking B vitamins might help slow brain shrinkage in older people with mild memory problems—but only if they also have enough omega-3s in their body. If they don’t, the B vitamins might not help as much.

We analyzed two assertions about omega-3 fatty acids and B vitamins in older adults with mild memory problems, and both point to a possible interaction between the two. What we’ve found so far suggests that neither omega-3s nor B vitamins alone appear to slow brain shrinkage in this group — but when they’re both present, there may be a combined effect. One assertion shows that B vitamins might help reduce brain atrophy only if omega-3 levels are already sufficient [1]. Another shows that high omega-3 levels in the blood may help slow brain shrinkage only when B vitamins are also being taken [2]. In both cases, the benefit seems to depend on the presence of both nutrients. There is no evidence in our review that either one works on its own in this context. The evidence we’ve reviewed leans toward the idea that the two work together, not independently. We don’t know why this interaction happens, or how much of each nutrient is needed, or how long someone must take them to see any effect. We also don’t know if this applies to people without mild memory problems. The data we’ve seen comes from just two assertions, both supporting the same pattern, but we don’t have details on study size, duration, or participant differences. For now, if someone is concerned about brain health and has mild memory issues, it may be worth considering whether both nutrients are part of their routine — but we can’t say this will definitely help, or how to best combine them.