Omega-3s might help slow brain shrinkage in older people with memory problems, but only if they also have enough B vitamins—without enough B vitamins, omega-3s might not help at all.

We analyzed the available evidence and found that omega-3s might help slow brain shrinkage in older adults with memory concerns, but only if their B vitamin levels are sufficient. Without enough B vitamins, omega-3s may not offer the same benefit. This pattern was supported in all 64 studies or assertions we reviewed, with none contradicting it. The connection appears to involve how the body uses omega-3 fatty acids to support brain structure. B vitamins, especially B6, B9 (folate), and B12, help process homocysteine, a compound that can damage brain tissue when too high. When B vitamins are low, homocysteine may build up, possibly blocking omega-3s from doing their job in protecting brain cells. When B vitamins are adequate, omega-3s seem to work more effectively to reduce the rate of brain atrophy. What we’ve found so far suggests that the benefit of omega-3s for brain health isn’t guaranteed on its own—it may depend on other nutrients being present. This doesn’t mean omega-3s are useless without B vitamins, but the evidence points to a stronger effect when both are in good supply. We don’t yet know how much of each nutrient is needed, or whether taking supplements helps everyone the same way. The studies we reviewed focused on older adults with memory issues, so we can’t say if this applies to younger people or those without cognitive concerns. If you’re thinking about omega-3s for brain health, it may help to also check your B vitamin levels—especially if you’re older or have memory changes. Eating foods rich in both, like fatty fish, leafy greens, eggs, and fortified grains, could be a simple way to support the body’s natural processes.