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Endo: First Blood

Before I get into the latest post, some exciting news! I’m going to be joining the Greaves Lab at the University of Warwick this September. It’s a new research group that will be looking at how different types of immune cells in women with endometriosis contribute to pain and endometriosis lesion formation. It’s an exciting time and I can’t wait to see what the project uncovers – I’ll be sure to post updates here as and when we make new discoveries! Anyway, onto our regularly scheduled programming.

If you have endometriosis, when did you first notice its symptoms? The answer to that question can vary quite a lot between individual people – some notice from the beginning of their first period, and while menstruation and endometriosis are not mutually exclusive (as it can rarely occur in women who don’t menstruate, postmenopausal women and men), for a very large number of people the link between the beginning of their periods (called the menarche) and endometriosis symptoms is undeniable.

The reason I’m talking about menarche today is that some studies (but not others) have suggested that girls who start their periods earlier, have an increased risk of endometriosis. This has led to more research into the relationship between endometriosis and menarche.

One such study (which you can read for free here) was published recently looking at the different types of endometriosis and whether they could be linked to age at menarche. This study took data from 789 women with endometriosis and divided them by type of endometriosis. This resulted in three groups: 199 women with superficial disease, 254 women with ovarian endometriosis and 336 women with deep infiltrating endometriosis.

The researchers then divided all these groups further into those that had an early menarche (i.e. less than 11 years old), typical menarche (i.e. between 12 and 13) and late menarche (after 13) and compared the different types of endo to the different ages of menarche. The diagram below shows the results of their analysis as the percentage of women in each group.

As you can see, within each type of endo there’s not much difference. The authors of this study analysed this data and found that there was no statistical difference between the groups, so there was no relationship between what age a girl starts her period and what type of endo she might be diagnosed with.

Studying the relationship between endo and menstruation however, is not a simple matter; the age at which a girl starts her periods is a complex mix of genetics and environment, so there are many factors that can influence it.

In a study of girls in England during the 1980’s, only 0.8% reported starting their periods by the age of 10, this increased to 3.6% by the age of 11, and increased even more to 21.7% by the age of 12. Cultural differences also need to be taken into consideration. A 2011 study of London schoolgirls found that the number of girls reaching menarche by age 11 was similar between white, black Caribbean and mixed heritages. However, far less girls from Asian and black African backgrounds had reached menarche by the same age. If you’d like to read a really interesting paper on how menarche varies with ethnicity, check out this one looking at menarche in 24 different ethnicities in China.

Yet another factor to consider is diet; another British study found a diet high in meat, protein and polyunsaturated fatty acids during the ages of 3-7 was associated with an early menarche. Then there is birth year to consider too; a recent paper looking at age of menarche in girls in Mexico found that from the 1940’s to the 2000’s the average age of menarche has decreased continuously, a trend that has also been observed in Canada, Spain, India, Japan, Russia, Turkey and several other countries.

What’s so special about menstruation that it keeps being linked so closely with endometriosis? Obviously many women with endo experience a worsening of their symptoms around the time of their period, but how does one relate to the other.

Endometriosis is dependent on hormones, mostly estrogen, which is the reason why so many medical therapies either try to limit (like with the contraceptive pill), or dramatically reduce (like with GnRH agonists) estrogen production in the body. Although the body produces hormones at a certain low level from birth, it is only during puberty that hormone production really ramps up, and this includes an increased production of estrogen.

There are several schools of thought as to why this is important for endometriosis. Because endometriosis is similar to the normal endometrium (which is shed during menses), some think that normal endometrial cells go ‘backwards’ during a period (i.e. up through the fallopian tubes and out onto the pelvic organs) where they settle and implant to form endometriosis lesions. Other think that endometriosis is something you are born with, and the onset of menses means that the accompanying rise in estrogen production stimulates the dormant endometriosis to grow and become active.

No one knows for sure which one of these schools of thought are correct, or if any of them are correct. Scientific investigations are constantly underway to try and answer this and many other questions that still remain about endometriosis.

Title photo by GEORGE DESIPRIS from Pexels

Graphics made in Canva

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Dr Matthew Rosser

I have over 15 years experience researching endometriosis, endometrial cancer and fibroids. During this time I have       noticed that whilst research is regularly published on               endometriosis very little is reported accurately to the public in mainstream media. This blog aims to educate and inform anyone who wishes to learn more about the science and research into endometriosis.


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