Recently, we reported that exposure to light at night caused tamoxifen resistance in an animal model of breast cancer. Now this work has been expanded to include the effects of exposure to light at night on treatment with the chemotherapy drug Adriamycin (doxorubicin).

Melatonin protects against serious Adriamycin-induced side effects

Heart damage (cardiomyopathy) is perhaps the most serious potential side effect of Adriamycin since it can lead to short-term or long-term heart failure. One study using a rat model of breast cancer reported that melatonin reduced Adriamycin-induced oxidative damage in heart cells. Another study reported that melatonin helped prevent the low blood platelet count, neurotoxicity, and fatigue that can be associated with Adriamycin treatment, while at the same time improving survival.

Melatonin and light at night

Melatonin is produced at night (or in conditions of darkness) and nocturnal light disrupts melatonin synthesis. When women work at night or are otherwise exposed to light at night, their risks of breast cancer and its recurrence increase. Perhaps the most dramatic evidence of this phenomenon is the finding that blind women have a lower risk of breast cancer than sighted women. In addition, total visual blindness provides significantly higher protection against breast cancer than partial blindness (i.e., with some perception of light).

Habitually sleeping in the presence of artificial light could promote breast cancer by inhibiting melatonin production. Blue light wavelengths appear to have a far greater suppressive effect on melatonin production than red wavelengths. In an Israeli study, 1,679 breast cancer patients were interviewed regarding bedroom light levels, including light coming in the room outside the bedroom and sleeping with the television on. "Sleeping habitat" light intensity was found to be linked to breast cancer risk.

Ensuring adequate melatonin levels

Women can maximize their melatonin production by minimizing sources of light in the bedroom (using a red light when light is necessary) and avoiding extended periods of night shift work. Melatonin levels can also be increased by consuming foods that incorporate melatonin. Common foods that are very good dietary sources of melatonin include almonds, cherries (especially sour or tart cherries), and tomatoes. Walnuts, oats, and sweet corn also contain some melatonin. Other very good sources of melatonin include white and black mustard seeds, sunflower seeds, fennel seed, red, brown and green algae, and flaxseed. Red meat consumption has been shown reduce circulating melatonin.

Melatonin supplements are normally taken to aid sleep or as part of an anti-aging regimen. Although such supplements have been shown to be effective in increasing circulating melatonin levels, there have been few studies concerning the impact of such supplementation on breast cancer risk or breast cancer recurrence. Safe and effective dosages for breast cancer survivors have not been established, although several studies used 20 mg once per day before bedtime. Please check with your oncologist for advice with respect to taking melatonin.

Latest research finds melatonin counteracts Adriamycin resistance caused by light

Data recently presented at the 13th Annual AACR International Conference on Frontiers in Cancer Prevention Research in New Orleans demonstrated that supplemental melatonin reduced the negative effects of exposure to light at night in rats bearing human breast tumors. Exposure to even low levels of light at night made the tumors resistant to Adriamycin. In fact, melatonin not only prevented the development of Adriamycin resistance but also promoted tumor regression.

To conduct the study, rats were exposed to 12 hours of normal light followed by 12 hours of dim light (during normal night time hours). Half of the rats were given melatonin supplements during the dim-light period. Rats that did not receive melatonin experienced tumor growth that was 2.8 times faster than that of rats receiving nighttime melatonin. Furthermore, dim light at night caused complete resistance to Adriamycin in the tumors of rats that did not receive melatonin, whereas tumors of rats in the melatonin group remained sensitive to doxorubicin and shrank rapidly. The authors found that tumors from rats that did not receive melatonin had significantly elevated levels of (1) two enzymes that break down Adriamycin to a less active form; and (2) membrane proteins that transport Adriamycin out of cells. The authors conclude that melatonin helps maintain active Adriamycin in tumor cells, whereas exposure to light at night, which suppresses melatonin production, has the reverse effect.

According to professor Steven M. Hill, breast cancer and circadian clock researcher at Tulane University School of Medicine in New Orleans, "although our research is very promising, it is not at a point where we can make recommendations to breast cancer patients taking either tamoxifen or doxorubicin about melatonin supplementation." He also noted that "taking melatonin supplements at the wrong time of day would potentially disrupt the natural melatonin cycle, which may, in itself, impair breast cancer responsiveness to tamoxifen and doxorubicin." However Hill was willing to make the recommendation that breast cancer patients "follow a natural light/dark cycle as much as possible, try to sleep or stay in a completely dark room during the night, and/or use a sleep mask."

Please see our article on what to eat during Adriamycin treatment for more information on how to optimize treatment and reduce side effects.