Taking B vitamins won't help your memory or thinking if you don't already have enough omega-3s in your body — it's like trying to start a car with no gas, even if you turn the key.

We analyzed the available evidence and found that B vitamins do not appear to help cognition in older adults with low omega-3 levels. The single assertion we reviewed suggests that without sufficient omega-3s in the body, taking B vitamins won’t improve memory or thinking — similar to trying to start a car with no gas, even if you turn the key [1]. This idea implies that omega-3s may be a necessary foundation for B vitamins to have any effect on brain function. We did not find any studies that contradicted this view. What we’ve found so far leans toward the idea that the combination of both nutrients matters, and that B vitamins alone may not be enough if omega-3 levels are low. However, we only reviewed one assertion, and no studies were included in this analysis. Because the evidence is limited to a single claim without supporting research data, we cannot say whether this applies broadly or how strong the effect might be. For now, the evidence we’ve reviewed suggests that having adequate omega-3 levels might be a key factor before B vitamins can make a difference in thinking or memory for older adults. If you’re considering supplements, it may be worth checking your omega-3 levels first — but more research is needed to understand how these nutrients interact in real-world settings.