IT takes just one year for couples to lose passion in their relationship - but you can talk your way out of it.
A study of more than 10,000 people found women's interest in sex tends to die down after a year living with the same partner, when sexual apathy among women quadruples.
The British National Survey of Sexual Attitudes and Lifestyles reveal 34 per cent of women and 15 per cent of men lack interest in sex.
And while desire among women declines significantly with age, male sex drive fell far more gradually - men tend to stay interested well into their 70s.
University of Glasgow senior research fellow Dr Kirstin Mitchell said her research showed both men and women who found it easy to talk about sex with their partner tended to have a better sex life.
"The findings ... emphasise the importance of providing a broad sexual and relationships education rather than limiting attention only to adverse consequences of sex and how to prevent them," Dr Mitchell said.
Sydney-based sex and relationship therapist Cyndi Darnell said desire can evaporate if a relationship is only based on lust but long-term sexual desire was more complicated.
"Lust is only one reason people have sex … the reasons people have sex is because they feel obliged to, because it's the glue for the relationship, the partner wants it and occasionally it's because they're horny," she said.
Zanna and Casey Faets, 26 and 27, have been together for nearly seven years and married for two years next month.
Both have always been very attracted to one other and say passion is all about confidence.
"When you're feeling confident and good about yourself, then the relationship and your love life stays exciting," Mrs Faets said.
"And you make sex a priority, especially on your date nights. Or spice up the relationship with nice lingerie. When you're not doing things for each other, you lose the spark."
Having maintained their relationship well beyond one year, they have no concern about the "seven year itch" because they are also best friends.
"We have a lot in common in terms of goals, businesses and outlook on life. We still have so much fun together," Mrs Faets said.