The secret of being born lucky is a summer birthday, with May babies most likely to enjoy a lifetime's good fortune, according to a study of more than 40,000 people.

The time of year at which you are born has an enduring influence on levels of optimism and self-reported luck, according to research by British and Swedish scientists.

May was the luckiest month in which to be born, with 50 per cent of those born then considering themselves lucky, while October was the least lucky month, with just 43 per cent claiming good fortune.

The findings add to growing evidence that the phenomenon of luck is not all down to chance, but is affected¹ by a person's general disposition².

Other research has shown that whether people think themselves fortunate depends less on objective success than on having a "glass half-full" or "half-empty" approach to life.

"What we are seeing suggests that something is influencing how people perceive their luckiness. My hypothesis is that people create their own luck by traits such as optimism, that luck is a psychological phenomenon rather than a matter of blind chance," said Professor Richard Wiseman, who led the research,.

The pattern of the results, with those born in spring and summer reporting themselves luckier than those born in autumn or winter, could have two potential explanations, Professor Wiseman said.

"One theory is a medical, physiological³ one, that the temperature at the time of birth might influence the development of the brain, particularly neurotransmitter chemicals," he said. "The pattern is the same as that you see in the depression literature: people born in the winter are statistically⁴ more likely to suffer from depression, and we may be seeing the same effect here."

"The other strong possibility is that mother-infant interactions are affected by seasonal⁵ factors. There is more post-natal depression in the winter, and mothers who suffer from this don't interact with their children in the same way. It's possible that this affects the psychological complexion⁶ of their children later in life."