A study has found fish oil capsules on sale in New Zealand could have half of the omega-3 fatty acids they claim to.
Researchers from the Canterbury University tested capsules bought from stores and found many were lacking in the acids DHA and EPA.
- Pregnant women told 'don't take fish oil' after 'dramatic' finding
- Fish oil supplements more like snake oil - study
- The breakdown on collagen: What's all the hype?
Lead author and Canterbury University psychology professor Julie Rucklidge told The AM Show a success rate of 40 percent is actually better than the capsules used to do.
"This was done a few years ago, a group at the Liggins Institute actually [did a] study showing that 10 percent of the ones that they studied were true to label.
"It's gotten a little bit better over the last few years, 40 percent of them were true to label, but 60 percent of them were between 48 percent to 89 percent of what they should have been."
Prof Rucklidge said she's not able to say if the capsules studied were true to label at some point and simply degraded over time, but it's not good enough.
"It should be accurate to label absolutely, especially given an expiry date and a shelf life so it should be able to maintain that."
There was some good news in the study though, the researchers checked to make sure they were safe for consumption.
"There was no detectable mercury in any of the capsules that we had analysed for mercury," Prof Rucklidge said.
The research has been published in the New Zealand Medical Journal.