For women, certain times of the month can be characterised by intense irritability, mood swings and food cravings.
Now, a study shows you really can blame your period for feeling rubbish.
New research indicates there are changes in the function and structure of the brain in women suffering severe cases of premenstrual syndrome, also known as PMS.
Louise Stiernman, a doctoral student from Umeå University in Sweden, conducted several studies involving women with premenstrual dysphoric disorder (PMDD), which is form of severe PMS.
Brain scans of women taken at different times of the month have revealed those with severe PMS have unique changes in areas involved with emotion during their period.
 She used MRI scans to follow the activity in different parts of the brain during different times of the month.
Analysis revealed women with PMDD had increased activity in parts of the brain that are linked to assessing the emotional significance of things.
This region is also important for co-ordinating appropriate behavioural responses.
The pattern was evident just before menstruation – the time referring to around a week before a woman’s period starts.
Investigations also showed the thickness of a part of the brain called the cerebral cortex was thinner in women with PMDD, indicating more long-lasting effects on the brain.
Up to a third of UK women have PMS, which can involve feeling depressed, irritable, bloated and anxious during menstruation, as well as tender breasts and spotty skin.
Ms Stiernman said it is possible that underlying differences in the brain structure and function in women with PMDD may make them more vulnerable to experiencing severe mood symptoms.
‘The results bring us closer to a biological explanation for why women with severe PMS are more prone to have strong emotional reactions to things in their environment during the premenstrual phase,’ she said.
She added that the findings do not make clear what is cause and what is effect, and it could be that recurring PMS symptoms are what affects how the brain is composed and how it functions.
It is estimated that as many as 30 per cent of women in the UK have moderate to severe PMS, while 5-8 per cent have PMDD.
Symptoms can include a depressed mood, hopelessness, mood swings, sudden tearfulness, increased irritability and anger.
Ms Stiernman’s findings are presented in her doctoral thesis.
