So much for tipping the scales.

In the long-running debate about whether fish oil supplements are helpful, harmful or hooey, new research on their effectiveness in preventing dementia offers … mixed results.

Neurology specialists from the Oregon Health & Science University (OHSU) say most older adults likely won’t benefit from fish oil supplements, but they may be worthwhile for people with a genetic predisposition to Alzheimer’s disease.

The study, published on Thursday in JAMA Network Open, followed 102 healthy adults who were dementia-free and at least 75 years old.

At the outset, they had relatively high levels of white matter lesions in the brain, a risk factor for dementia, and relatively low blood levels of brain-beneficial omega-3 fatty acids, which are found in fish oil.

Half of the participants took daily fish oil supplements rich in omega-3 while the rest took a soybean oil placebo.

The participants underwent scans at the beginning and end of the three-year study to assess changes in the lesions.

For the most part, there was not a statistically significant difference between the fish oil and placebo groups.

“I don’t think it would be harmful, but I wouldn’t say you need to take fish oil to prevent dementia,” said study author Lynne Shinto, professor of neurology at the OHSU School of Medicine.

However, OHSU scientists found that carriers of the APOE4 gene who took the fish oil experienced a dramatic reduction in the breakdown of nerve cells in the brain.

The change was noticeable as soon as one year after starting fish oil treatment.

Now, researchers are calling for a larger, more diverse trial to test fish oil’s effect on people with APOE4, which is a major genetic risk factor for late-onset Alzheimer’s.