June 19, 2014

expert reaction to study on UV addiction in mice

A study published in the journal Cell reported that rats released endorphins when chronically exposed to ultraviolet (UV) radiation, leading to physical dependence, tolerance, and addiction-like behaviour.

Dr Clare Stanford, Reader in Experimental Psychopharmacology at UCL (University College London) said:

“This study does not provide the sort of evidence needed to show addiction to UV light in mice and it is even less certain that the work predicts addiction in humans. This would require testing whether the mice preferred UV light or non-UV light, which was not done in this paper.

“The strain of mice used in this experiment produce virtually no melatonin, which is thought to protect against damage from UV light. Shaving such mice and exposing them to UV light raises important ethical questions about animal welfare and again casts doubt on the relevance of the results to humans.

“The paper suggests that beta endorphin in the skin may be active in melatonin-deficient mice in UV light, producing a favourable response. However, there is no evidence of UV addiction, nor any suggestion that a measurable effect would be seen in normal mice, let alone in humans.”

Dr Richard Weller, Senior Lecturer in Dermatology, University of Edinburgh, said:

“I would first say that mice are nocturnal animals, covered in fur, which avoid the light so one must be cautious about extrapolating from these experiments to man.

“Nonetheless, the authors discuss some literature suggesting that a similar pathway might also be present in man. It is very unlikely that evolutionary pressures would select for a trait which reduces survival and reproductive ‘fitness’. If an ‘addiction’ to sun truly also exists in mankind, it suggests to me that there is a benefit to it. The authors mention Vitamin D, but in addition to this, epidemiological data (particularly from Scandinavia) show that increased sun exposure is associated with reduced all-cause mortality. Our recent work shows how sunlight reduces blood pressure independently of vitamin D, which may account for some of the health enhancing effects of sun.”

‘Skin b-Endorphin Mediates Addiction to UV Light’ by Fell et al. published in Cell on Thursday 19^th June.

Declared interests

None declared