In fact, men who were randomly assigned to take fish oil actually ended up with an increased risk of depression symptoms.

The researchers caution, however, that it's not clear whether the fish oil is to blame. For now, they say, there's no evidence to support using fish oil or B vitamins to ward off depression.

What's more, it's not clear if people with cardiovascular disease should routinely use the supplements for any reason.

"Generally, it should be stressed that the dietary supplements that we studied are in fact active substances that, when taken over a long period and without a physician's advice, might not have positive effects on health," lead researcher Valentina A. Andreeva, of the University of Paris, said in an email.

And in fact, she added, long-term supplement use might have "adverse effects" in some people.

Studies have found that people who suffer depression after a heart attack or stroke tend to fare worse than their non-depressed counterparts. Researchers aren't sure why that is, but the findings have sparked interest in finding ways to prevent depression in heart disease and stroke survivors.

Fish oil has seemed like a good candidate because it's rich in omega-3 fatty acids, which are thought to be good for the heart -- and possibly for mental well-being.

Similarly, B vitamins could be helpful, in theory. Deficiency in the B vitamin folate, for instance, has been linked to a decline in the mood-regulating brain chemical serotonin.

But in the new study, Andreeva's team found that giving patients supplements -- of B vitamins, fish oil or both -- did nothing to prevent depression symptoms over nearly five years.

The findings, reported in the American Journal of Clinical Nutrition, are based on 2,000 middle-aged and older adults who'd suffered a heart attack, stroke or severe chest pain caused by clogged heart arteries.

Each was randomly assigned to one of four groups: one that took a mix of folate and vitamins B6 and B12 each day; one that took fish oil capsules; a third that used fish oil and B vitamins; and a fourth given placebo capsules.

Over the next three to five years, almost one-third of the study group had some degree of depression symptoms. And about seven percent were found to have moderate to severe depression.

There was no evidence that the risk was any lower for people who'd been on B vitamins or fish oil, versus the placebo group. But among men, those on fish oil were 28 percent more likely to develop some level of depression symptoms.

It's not clear what to make of that, the researchers say.

They point to another recent clinical trial that tested fish oil for preventing depression in older adults. And while those researchers found no benefits, they also found no increased risks.

For now, there appears to be no reason for people with a history of heart disease or stroke to routinely use fish oil or B vitamins.

Andreeva said that in earlier reports on this same study group, the researchers found that neither supplement cut the risk of future heart problems or stroke. Nor was there any evidence the supplements curbed cancer risk.

And another recent report, which combined the results of 14 past studies, reached similar conclusions: There's no clear evidence that fish oil prevents heart attacks or strokes in people with existing heart disease.

That does not, however, mean you shouldn't eat fish.

In fact, the American Heart Association and other groups recommend that people eat fish at least twice a week -- preferably fattier varieties, like salmon and tuna, that contain more omega-3.

Andreeva agreed on the importance of a healthy diet -- which also includes plenty of fruits and vegetables, fiber-rich grains and low-fat dairy.

As for preventing depression post-heart attack or stroke, it's not certain what works.

But Andreeva said that in general, it's thought that a healthful lifestyle -- staying physically active and not smoking, for example -- may help. There's also evidence that staying socially active offers a buffer against depression.

SOURCE: bit.ly/LILOBA American Journal of Clinical Nutrition, online May 30, 2012.

• A Permanent Economic Emergency