A Japanese mother holding her baby is seen in this August 6, 2005 file photo.

"More sex." That's what one expert says is needed to solve Japan's baby shortage.

"Japanese people simply aren't having sex," Dr. Kunio Kitamura, director of the Japan Family Planning Association said.

An association survey of 936 people between the ages of 16 and 49 showed 31 percent had not had sex for more than a month "for no particular reason" -- a condition known as "sexless."

"As much as subsidies and welfare programmes are important, sexlessness is also a critical issue in this problem."

Japan's fertility rate -- the average number of children a woman bears in her lifetime -- fell to an all-time low of 1.25 last year. Demographers say a rate of 2.1 is needed to keep a population from declining.

Japan came last among 41 nations in a poll last year by condom manufacturer Durex, with lovers there having sex just 45 times a year compared to a global average of 103 times a year.

Kitamura said that while many men in workaholic Japan are simply too "stressed out" from their jobs to have enough energy for sex, many other couples simply do not have sex regularly.

In the association's survey, 44 percent of the people who said they weren't having much sex felt that having a relationship with the opposite sex was "very tiresome" or "tiresome."

Kitamura's advice? Couples should talk to each other.