Research findings announced yesterday indicate that the kind of lighting used in fertility clinics can affect whether embryos successfully develop into babies.

Sunlight and cool-white fluorescent lights were found to cause the most damage to mice embryos, even when the exposure was limited to a few minutes, said Dr. Ryuzo Yanagimachi, a retired University of Hawai'i researcher who is internationally renowned as a pioneer in reproductive biology.

"We found that warm-white light is less damaging," Yanagimachi said.

Cool-white fluorescents, which are blue-white in appearance, are the most common lighting found in offices, while warm-white lights, with a yellow-white color, are popular in residential settings.

He said laboratories that work with animal or human embryos should consider the kind of lighting used in work spaces. He also suggested improving techniques so exposure to light is minimized during egg collection and insemination, and while fertilized eggs are examined before being transferred back into the womb.

"People do not pay much attention to light as a negative environmental factor," he said.

Yanagimachi worked on the study with Manami Takenaka and Toshitaka Horiuchi of the Prefectural University of Hiroshima. He said the notion that light could affect the development of embryos first arose 20 years ago while conducting other research with hamsters, whose fertilized eggs proved especially vulnerable to light damage.

Mice embryos are less sensitive, and Yanagimachi and his colleagues found that exposing the animal's fertilized eggs to direct sunlight, even for just 10 seconds, caused the most damage. The study also showed that when comparing embryos exposed to cool-white and warm-white fluorescents, "far more" of the warm-white eggs developed into babies, he said.

Damage occurs when the light exposure places stress on the embryo, which responds by producing increased levels of radical oxygen that are toxic to cell structures, according to Yanagimachi.

Scientists suspect that fish and frog eggs have some sort of mechanism that protects them from sunlight damage, but that embryos from mammals, which develop in the safety of a darkened womb, lack the protective mechanism, he said.

Different species have different tolerances for light damage, and although the experiments were limited to fertilized animal eggs, Yanagimachi said it is likely human embryos also can be affected by light.

Red lights commonly used in photography darkrooms are not suitable for clinical work, Yanagimachi added. "We cannot work in darkness," he said.

Lighting is a matter of personal taste, but even before his study, Yanagimachi said he preferred warm-white light for his work, which has included cloning a mouse in 1998 and creating three generations of mice from the first clone.

The latest findings are published in the Aug. 13 issue of Proceedings of the National Academy of Sciences of the United States of America.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.