More than 33,000 men and women between the ages of 16 and 44 took part in the UK-based study, which involved three successive surveys between 1991 and 2012.
The researchers found the steepest declines in sexual frequency occurred in those aged 25 and over, and in those who were married and cohabiting.
But more than half of the women and two-thirds of men surveyed also admitted to wanting more sex.
The research hypothesised the decline coincided with two events of possible importance - the introduction of the iPhone in 2007, and the global recession of 2008.
But the most compelling explanation, given the age and marital status of those affected, related to the stresses of modern life, as work, family and leisure are constantly being juggled.
While the research was conducted out of the UK, the trends match those in other countries, including Australia.
Declines in sexual frequency have also been reported in Finland, the United States, and Japan.
An Australian study conducted in 2014 found that 85 per cent of men and 69 per cent of women wanted to have sex more often than they actually did.
That said, while couples were having sex less often, there was an increase in the variety of their sexual encounters.
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This article originally appeared on 7News