Taking omega-3 supplements every day for six months doesn’t seem to help people with mild to moderate Alzheimer’s think better, no matter what their blood homocysteine levels were to begin with.

If you have Alzheimer’s and your blood has high levels of a substance called homocysteine, taking omega-3 fish oil supplements might help your memory and thinking skills a bit—but only if you look at certain tests, not all of them.

For people with early-stage Alzheimer’s, taking a specific fish oil supplement for 6 months might help them think a little better and function more normally—but only if their blood has low levels of a chemical called homocysteine before they start.

Taking omega-3 supplements might help people with Alzheimer’s do better on some memory and thinking tests, but not all of them—so the benefits aren’t the same for every type of brain function.

Taking a specific daily dose of omega-3 fish oil for six months may help people with early-stage Alzheimer’s think a little better and function more normally—but only if their blood has low levels of a substance called homocysteine.

People with Alzheimer’s who have low levels of a substance called homocysteine in their blood might respond better to omega-3 supplements than others, and their B vitamin levels could be why.