A new study has found that consumption of fish oil supplements might make chemotherapy treatment for cancer less effective. But a recent survey has found that many cancer patients were taking those supplements.

According to the researchers, all six of the studied supplements of fish oil had a specific fatty acid that has been uncovered to lower the effectiveness of chemotherapy in mice.

Lead study author Dr. Emile Voest, from the Netherlands Cancer Institute in Amsterdam, said that the cancer patients receiving chemotherapy must refrain from taking fish oil supplements and consult any supplement with their doctors.

“I’m always discussing it with my patients. Please have an open relationship with me and tell me what you’re taking,” Voest said.

The researchers said that omega-3 fatty acids are consumed by nearly a fifth of Americans with cancer, generally through fish oil. Fish oil is often available for use in form of capsules for roughly USD 10 or USD 11 for 100 pills.

It was earlier uncovered that even a small amount of two fatty acids lowered the efficacy of chemotherapy in mice having cancer. Voest said that these fatty acids is likely enable cancer cells for repairing themselves faster after chemotherapy.

When the researchers looked at the two fatty acids present in six fish oil supplements, they failed to detect one. But the other fatty acid, known as 16:4(n-3), was ubiquitous in the supplements.

400 people were also surveyed by the researchers who were receiving cancer treatment in November 2011. 35 percent of the 118 people who returned the surveys were found using nutritional supplements, while 11 percent reported using supplements of omega-3 fatty acid.

Oncology nutrition expert Stacy Kennedy, from Dana-Farber Cancer Institute in Boston, says people must be cautious while going overboard with avoiding all omega-3 fatty acids. This is all because fatty acids form an essential part of the diet.

The findings of the study were published in the journal JAMA Oncology.