The Consumer Council on Tuesday warned that some health supplements may not be as healthy as they appear, after it found contaminants or carcinogens in some popular fish oil products on sale in Hong Kong.

The watchdog tested 25 fish oil samples and found that all of them had some type of contaminant.

All but one were found to have the chemical 3-MCPD, with three exceeding European Union safety standards. Fourteen samples were also found to contain the genotoxic carcinogen glycidol.

"In the experimental animal data, we found that it [3-MCPD] will affect our kidney, our central nervous system and also the male reproductive system. So this is something that should not be in our products," said Nora Tam, chairwoman of the council's research and testing committee.

In one product from Adrien Gagnon, the level of both glycidol and 3-MCPD exceeded European Union safety standards. The council has referred the product to the Centre for Food Safety for follow-up action.

Meanwhile, the council said it found discrepancies between content levels of omega-3 fatty acids and the declared values on nutrition labels.

In two fish oil products for children and pregnant women, the amount of DHA - an omega-3 fatty acid - fell short of the labelled value by 70 percent.

Tam reminded consumers that these nutrients can be absorbed through their regular diet.

"For omega-3 fatty acids, they are available in a lot of food, particularly fish. So you have to think twice: Do you really need to take this supplement? The best is eat the fresh food materials, so you don't need to rely all the time on supplements to get omega-3 fatty acids," she said.

The council urged manufacturers to improve product quality and label their products accurately to safeguard consumers' health.