- New study has found light shining through the curtains at night could suppress the production of melatonin
- Scientists found it stopped the cancer drug tamoxifen from working
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Dim light exposure through the curtains from street lights can make certain cancers resistant to the drug tamoxifen
Street lights shining through curtains at night could stop breast cancer drugs from working effectively, new research has suggested.
The study found dim light exposure can make certain cancers resistant to a drug called tamoxifen, by suppressing melatonin production.
The research failed to quantify exactly how much light exposure is needed to suppress the levels, but the team believe the light seeping through the curtains from the street could be enough.
Scientists found by giving rats a melatonin supplement during the night, they could overcome the negative effects.
Professor Steven Hill, from Tulane University School of Medicine in the U.S., said: ‘Resistance to tamoxifen is a growing problem among patients with hormone receptor-positive breast cancer.
‘Our data, although they were generated in rats, have potential implications for the large number of patients with breast cancer who are being treated with tamoxifen.
‘They suggest that night time exposure to light, even dim light, could cause their tumours to become resistant to the drug by suppressing melatonin production.
‘Our study does not identify how much light exposure is needed to suppress night time melatonin production, and potentially drive tamoxifen resistance in humans, but we think that it could be as a little as the amount of light that comes in the bedroom window from a street light.
‘We are working toward conducting the studies that will answer this question.’
He added that although melatonin supplements are readily available over-the-counter at most pharmacies, the research is not at a point where a general recommendation should be made that breast cancer patients taking tamoxifen should go out and buy melatonin.
‘Melatonin is produced by our bodies at a very specific time of day, exclusively during darkness at night,’ he explained. ‘Taking melatonin supplements at the wrong time of day would potentially disrupt the circadian system, particularly the natural melatonin cycle, which may, in itself, paradoxically impair breast cancer responsiveness to tamoxifen.’
The research, published in the journal of the American Association for Cancer Research, looked at rats living in 12 hours of normal light followed by 12 of dim light. They measured the melatonin levels in their blood.
It was revealed that for rats living in normal light dark conditions their melatonin levels rose during the dark period and decreased during the light.
However, for rats living in disrupted light conditions their levels remained low throughout.
Resistance to tamoxifen is a growing problem among patients with hormone receptor-positive breast cancer
And tumour growth for rats living in the dim light was 2.6 times faster than rats living in normal light.
Tumours were also completely resistant to tamoxifen in dim light, however this was reversed when the rat was given a melatonin supplement.
‘These data suggest that, in the not-too distant-future, it may be possible to combine melatonin and tamoxifen,’ said Professor Hill.
‘However, before this is done we would need to identify the optimal times of day to give the two because if the timing between the two is off, the advantage of giving them in combination may be lost.
‘This brings up another important point: Our levels of melatonin are not determined by sleep, as many people think.
‘It is actually the darkness that is important. During the night, if you sleep in a brightly lit room, your melatonin levels may be inhibited; however, if you are in the dark but cannot sleep, your melatonin levels will rise normally.’
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