The 'feel good factor' of Christmas causes a peak in the number of people having sex – resulting in a 'baby boom' nine months later, a new global study has found.

Researchers discovered a rise in sex-related Google searches over the festive period, which is linked to an increase in births later on in the year, the Daily Mail reported.

Interestingly, the same effect was not seen around Easter or other major holidays such as Thanksgiving in the US.

Experts say the focus on family, love and presents makes people feel more amorous in Christian countries in both the northern and southern hemisphere. 

For those of us on the other side of the world this Christmas, a previous study found that there is also a biological reason you're more likely to conceive when it's cold, because men produce better quality sperm in winter compared to summer.

The study drew upon data from nearly 130 countries that included sex-related Google search terms from 2004 to 2014 and 10 per cent of public Twitter posts from late 2010 to early 2014.

It found interest in sex peaks significantly during major cultural or religious celebrations – based upon a greater use of the word 'sex' or other sexual terms in web searches.

These increases were linked to a rise in births nine months later in countries with available birth-rate data, according to the scientists at Indiana University in the US and the Instituto Gulbenkian de Ciência in Portugal.

This was seen during major holiday celebrations of Christmas in Christian-majority countries and Eid-al-Fitr, the celebration that marks the end of Ramadan, in Muslim-majority countries.

The case of Eid-al-Fitr was significant because the holiday does not occur on the same day each year, but the measured effect still shifts accordingly, following a clear cultural pattern.

The researchers suggested the study revealed collectively people appear to feel happier, safer and calmer during the holidays. 

Professor Luis Rocha, of Indiana University, said: "We observe that Christmas and Eid-Al-Fitr are characterised by distinct collective moods that correlate with increased fertility.

"Perhaps people feel a greater motivation to grow their families during holidays when the emphasis is on love and gift-giving to children.

"The Christmas season is also associated with stories about the baby Jesus and holy family, which may put people in a loving, happy, 'family mood.'"

Past studies tended to focus on smaller geographic areas in the Western and Northern hemispheres.

Professor Rocha added: "The rise of the web and social media provides the unprecedented power to analyse changes in people's collective mood and behaviour on a massive scale.

"This study is the first 'planetary-level' look at human reproduction as it relates to people's moods and interest in sex online."

The study was published in the journal Scientific Reports.