Ask Dr Gary: Fat cells in hormone overdrive

Can you tell me more about PCOS? I'm 27, and after years of very irregular periods my doctor diagnosed me with it and told me I'd need a Mirena. He explained it to me, but I didn't exactly understand the reasons why PCOS occurs or how Mirena would help.

- DM

Polycystic ovary syndrome is common, affecting one in 15 women. Not all cases are weight-related, but most are associated with overweight or obesity-2 categories that encompass 65 per cent of the New Zealand population, according to Ministry of Health data. PCOS can be a cause and an effect of obesity, and reducing excess weight is a key (if hard to achieve) goal in managing PCOS for most.

Fat cells produce hormones - lots of them. Obese women can end up with very high levels of testosterone as a result of this overactive hormone production.

For a woman this can mean male-type hairiness, irregular periods, decreased fertility, diabetes, or ovaries that fail to release eggs. About a third of the time the ovaries end up covered in fluid-filled cysts, hence the name Polycystic Ovary Syndrome.

It's a surprisingly common finding when doctors look for it but, in most cases, it passes under the radar until a fertility issue arises or problem periods force a woman to seek medical care.

In healthy women, the normal monthly menstrual cycle involves thickening of the uterus lining, the release of an egg from an ovarian follicular cyst, then a shedding of the uterine lining (menstrual bleed) at the end of the cycle. With PCOS, ovulation (or the release of an egg from an ovarian follicle) doesn't occur normally, and the uterine lining gets more and more built-up. This predisposes the woman to irregular periods, and to increased risk of endometrial cancer later in life.

Mirena is an intrauterine device, placed by doctors, which releases tiny amounts of the hormone progesterone into the uterine lining to prevent it thickening excessively. This helps prevent irregular or heavy bleeding, and is thought to also decrease cancer risk.

Hope this information helps. See your GP too, to chat about the particulars of your case. Best wishes.