People would need to eat one to two portions of oily fish such as salmon, tuna or sardines each week to reduce their breast-cancer risk, according to the findings, the British Medical Journal said in a statement yesterday.
The study’s results confirm the World Health Organization’s recommendation to eat fish once or twice a week, Veronique Chajes, an epidemiologist at the WHO’s International Agency for Research on Cancer in Lyon, France, said in a phone interview. She didn’t give a recommendation to take fish oil supplements.
“The recommendation is really on fish consumption, not on supplements,” Chajes said.
Chinese scientists led by Duo Li of Zhejiang University in Hangzhou, China, pooled and analyzed data from 21 previously published studies that had enrolled 883,585 participants. They found that for each 0.1 gram or 0.1 percent energy increment of fish oils taken daily, the risk dropped by 5 percent. Plant-derived fatty acids such as alpha linoleic acid didn’t affect risk, the study said.
“This is a pretty sound result, we are very confident in this study,” Li said in a telephone interview. Polyunsaturated fatty acids “are very, very beneficial for human health.”
The individual studies tracked either how fish or other fish oil sources their participants consumed, or measured how much of the substances could be found in subjects’ fat or blood.
While the research was “high quality” and furnished strong evidence that fish oils may be beneficial, it doesn’t prove the link, Emily White, a researcher at the Fred Hutchinson Cancer Research Center in Seattle, Washington said in an e-mailed message.
“There may be some factor associated with health consciousness that associated with both eating high-omega 3 fish (e.g. salmon) and with reduced breast cancer risk, that was not controlled for in all studies,” White said. “Only a randomized trial can provide definitive evidence.”
The study belongs to a form of research known as a meta-analysis, which evaluates data from previous investigations without doing new clinical work.
Asian participants were shown to have the largest risk reduction, possibly because of the high level of fish consumption in Asian countries, the researchers said.
Humans can’t make omega-3 fatty acids from scratch, but need them for healthy brain function as well as growth and development. These acids can be found in fish as well as in foods such as walnuts and flaxseed.
A woman born in the U.S. today has about a one in eight chance of being diagnosed with breast cancer during her life time, according to the National Cancer Institute.
The study was funded by the National Natural Science Foundation of China, Ministry of Education of China and National Basic Research Program of China.
The authors said that they had no financial conflicts of interest.
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