Studio guest: Professor Josef Köhrle

a hormone researcher at Berlin's Charité University hospital.
DW-TV: We´re joined by Professor Josef Köhrle. As we saw in that report, artificial lighting can suppress production of the hormone melatonin. And there's actually a connection to cancer. Is research actually sure about that?


Josef Köhrle: Since a large international conference on this issue two years ago, there has been a lot of data collected suggesting that melatonin and the disruption of chronorhythms has an impact on cancer development and progression.


DW-TV: Do you have an explanation for how missing out on melatonin can cause cancer?


Josef Köhrle: We have no clear cause-effect relationships at the moment but we have associations. We are quite sure that melatonin promotes cell apoptosis. A lack of apoptosis will lead to the accumulation of tumor mass. We know that melatonin has an impact on cellular redox mechanisms. The lack of melatonin would probably increase the exposure and activity of reactive oxidants or free radicals. Thirdly, melatonin seems to interfere with a specific sub-group of receptors - especially the sex steroid receptors in the mammary gland and in the prostate gland.


DW-TV: Do I understand correctly that other hormones are involved in causing cancer or have an influence on cancer too?


Josef Köhrle: We know that several hormones tend to help tumor cell proliferation. But there are also many beneficial effects of hormones, which fight against the development of tumors and the carcinogenic process. We have to be very specific as to which hormone in which condition - sometimes it is positive, sometimes it is negative.


DW-TV: Man is interfering with its hormone levels. Do you think that is a good thing to do?


Josef Köhrle: I think that's not a good thing. It's not just the daylight rhythm that is being disturbed, also the nutrition rhythm is affected. Physical exercise has marked effects on the circadian rhythms. Then there is the cortisol rhythm and the stress rhythm. The light-night cycle has been very important in human evolution. We should not disturb it too much.


DW-TV: That means we should go back to a lifestyle like people had 100,000 years ago?


Josef Köhrle: Not necessarily. But we should not work against the sun or the night either. We should realise what our basic rhythms are. We need sleep. Sleep is essential. We need physical activity. This should not be at night, but rather during the day.


DW-TV: Thanks a lot for your time, Professor Köhrle.


Interview: Ingolf Baur