A It’s certainly true that some scientists are beginning to come round to the view that sunlight has many health-giving qualities, but the general consensus is still that the sun’s rays are harmful - after all, they can cause malignant melanoma, or skin cancer.

It’s a position that goes against the body of evidence going back to the early 1940s that suggests that regular exposure to sunlight can be protective against many cancers, including those of the breast, colon, ovaries and prostate (Cancer Res, 1995; 55: 4014-22). Sunshine may also prevent diabetes, multiple sclerosis (Toxicology, 2002; 181: 71-8; Lancet, 2001; 358: 1476-8), heart disease, osteoporosis and psoriasis.

For those of us living in sun-starved northern climes, we need to either supplement with vitamin D, cod liver oil or omega-3 fatty acids, or eat more oily fish, such as tuna and salmon (Neurology, 2004; 62: 60-5).

But the least-favoured alternative is to lie on a sunbed under ultraviolet-A (UVA) radiation. In the first place, it’s emitting the wrong type of waves if you wish to maintain good health. UV rays from the sun are divided into long-wave UVA (around 380-320 nanometres), medium-wave UVB (around 320-280 nm) and short-wave UVC (around 280-180 nm). UVA waves are responsible for tanning, while UVB activates the synthesis of vitamin D. UVC rays, which are mainly filtered out by the ozone layer, kill bacteria, viruses and other infectious agents.

A common problem with sunlamps, which has been found even in the controlled environment of a hospital clinic, is their correct calibration, and they can emit a far higher level of radiation than is considered safe. One study involving special clinics found that the UVA settings were out by as much as 18 per cent, and by up to 60 per cent for the UVB settings (Br J Dermatol, 2004; 150: 1162-6).

Furthermore, UVA sunbeds can double the risk of skin cancer. The risk seems to be greatest among young people who are still in their teens, according to a study of 900 skin-cancer patients (J Natl Cancer Inst, 2002; 94: 224-6). People who use tanning devices were 2.5 times more likely to develop squamous-cell skin cancer, and 1.5 times more likely to have basal-cell skin cancer. Other problems include photoageing (premature signs of age due to light) and poor immune function (Toxic Appl Pharmacol, 2004; 195: 298-308).

A better option during the long dark days of winter is full-spectrum (FS) lighting, which is claimed by its advocates to be as close as we can get to emulating natural sunlight. Ordinary light from standard lightbulbs or strip lighting contains no UV waves, whereas FS supports the full UV range. One study, in a classroom in Florida, concluded that FS lighting can strengthen immunity (Am J Psychiatry, 1987; 14: 1123-34), help to fight depression (J Affect Disord, 1998; 49: 109-17) and is effective against seasonal affective disorder (SAD) (Acta Psychiatr Scand, 1995; 91: 352-60). Sadly, however, there have been few other studies of the efficacy of FS lighting, with most of them having been carried out by the late biologist Dr John Ott, its most strident champion.