With commercial space flights in the pipeline and financiers appealing for a couple to volunteer for a manned (and womanned) mission to Mars, it's only going to be a matter of time before humans will want to do what we do best up in space.

But according to new research, getting down while we're way up high could theoretically cause health problems for spacefaring lovers.

James Bond may have given it a go in Moonraker, but experiments on mating plants by scientists at Montreal University show that weightlessness affects the way cells are transported inside living things, causing 'traffic jams' on the vital highways that connect different processes.

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Although researcher Anja Geitmann said they could not draw any specific conclusions on the implications for animal - and human - sex in space, she added that intercellular transport is important in a variety of human cells.

Geitmann told LiveScience.com that many neural disease, including Parkinson's, Alzheimer's and Huntingdon's are all related to this 'trafficking'.

Sex in space is thought to have to become a certainty, as it is unlikely the couple on the Mars mission will want to abstain for the entire 16-month trip.

Renowned physicist Brian Cox told Shortlist magazine this week that he and his wife would not be volunteering for the mission because "there are no restaurants on the way," so one might imagine that couples would be similarly reluctant knowing that one of their other marital pleasures was a no-go.

There is no firm boundary where space begins but the Kármán line begins at approximately 100 km (62 miles) above sea level and is used as the start of outer space for the purpose of space treaties and aerospace records keeping.