Scientists in the US have recently discovered that less time spent in leather, metal or oak beds could result in illnesses along the line. Researchers from Yale University have discovered that the circadian clock - the genetic system that regulates sleep on a day-to-day basis - is also linked to the level of TLR-9 in the body, which is vital to the immune system. TLR-9 was tested in mice to discover that when the gene was at its optimal amount, it responded better to bacteria and viruses, while the mice themselves were able to deal with infection and vaccinations much more effectively. In principle, this should also apply to humans. Reporting their findings in the journal Immunity, it was further argued that disruptions to this circadian rhythm can make people more likely to contract, or suffer worse from, illness. Issues that were of particular concern included jetlag and the timing of when people ought to receive vaccinations. Professor Erol Fikrig, who worked on the paper, said: "Sleep patterns of patients in intensive care are often disrupted because of the noise and prolonged exposure to artificial light. It will be important to investigate how these factors influence immune system response."