Thursday, 7 April 2016

Don't go Breaking my Heart

To my shame I haven’t managed to post much recently, normally I do a run of posts for Endometriosis Awareness Month in March but I haven’t been able to this year. To rectify this I’m going to be upping my posting frequency throughout the rest of the year as penance for my lack of posting thus far.

Chances are you may have seen a report from a recent piece of research about a link between endometriosis and an increase in risk in heart disease. It’s an attention grabbing article for sure, but what exactly is this new research telling us?

This week I’ll be going through the origin research article and dissecting exactly what the authors found.

This research was published in the journal of Circulation, Cardiovascular Quality and Outcomes in March of this year. The study enrolled 116,430 women in 1989 and followed them up over the course of 20 years with periodical questionnaires about their health. At the beginning of the study there were 5,296 women with laparoscopically confirmed endometriosis and 109,161 women without. By the end of the study the number of women with laparoscopically confirmed endometriosis had risen to 11,903.

At the beginning of the study when comparing things like age, BMI, contraceptive use, smoking, alcohol consumption, diet, and parents heart attack incidence, the groups of women with and without endo were very similar. Some real differences were noticeable when comparing the menopausal and surgical history of the two groups. More women in the endo groups were postmenopausal (14% vs 2%), had a hysterectomy (21% vs 4%), or had either one or both ovaries removed (17% vs 2%).

The main outcome of this study was to look for the rates of coronary heart disease (CHD) in these groups of women and compare them. In this case CHD was defined the occurrence of one or more of the following: heat attack (fatal or non-fatal), angina, coronary bypass graft surgery/angioplasty (repair or unblocking of a heart vessel)/stent (a device to keep the arteries to the heart open).

At the end of the study, in the endometriosis group, there were 69 cases of heart attack, 149 cases of angina, 91 cases of coronary bypass/angioplasty/stent and 207 cases of combined CHD.

After doing some fancy calculations and taking into account factors like age, smoking, diet etc the authors found that, overall, women with endometriosis were 63% more likely to have one of the CHD aspects than women without endo. When taking the individual CHD factors into account they found a 53% increase in heart attacks, 91% increase in angina and a 35% increase in coronary bypass/angioplasty/stent. Now those numbers seem pretty scary right? But they are relative. Consider the following example, if I tell you I’m going to increase your chance of getting struck by lightning by 100%, does that mean you are absolutely going to be struck by lightning? Nope, it would only mean that if I said I’m going to increase your chance of getting struck by lightning to 100%.

To work out how much your risk is increased you need to know the risk for the general population. Going back to our lightning example, the lifetime chance of getting hit by lightning (in the US) is 1 in 12,000 or 0.00008%. so if I increased your chance by 100% (which is the same as doubling it) your lifetime risk of being hit by lightning would still be only 0.00016%, still a really, really small chance. So it’s always worth knowing what the actual chance of having something happen to you is before worrying about an increase in risk. Unfortunately heart disease is not as rare as being hit by lightning, quite the opposite in fact.  Heart disease affects around 1 in 4 women and is the number #1 killer of men and women in most western countries. So whilst this study isn’t saying you are absolutely going to have a heart attack or angina etc, it does highlight that women with endometriosis appear to be at a higher risk of these things than the general population.

To tease out the effect this study divided the women into age groups of: under 40, 40-50, 50-55 and 55 and over. What they found was that women with endo in the 40 and under category were at a much higher risk of CHD.  Now this may be the case, but 40 and under is a quite a broad age range, particularly when you take into account that one of the age groups (50-55) was a very narrow range. There is a brilliant graph in the paper that shows how risk of CHD increases with age for women with and without endo. Unfortunately I can’t show it here without invoking the gods of copyright, which is a shame because this graph shows that at age 25, the risk of CHD for women with and without endo is pretty much the same. As age increases you can see risk of CHD does increase between the two groups. Just by looking at the graph itself the risk in CHD for endo sufferers appears most pronounced between the ages of 40 and 50. After age 55 the risk of CHD becomes the same again for both groups. So it is inaccurate to say that the risk of CHD is the same for a woman with endo who is 25 years old and a woman who is 40 years old.

The next question is, if this association exists, why? From the analysis that was done on this data, we know that factors like, diet, smoking, BMI (the common risk factors for CHD) were already taken into consideration, so there must be something else. One of the main contributing factors identified by this study is having a hysterectomy and oophorectomy. This effect has been observed in other studies too, which found that hysterectomy and oophorectomy before the age of 50 increases the risk of cardiovascular diseases. Women with endometriosis, particularly severe form of the disease, are more likely to have a hysterectomy and/or oophorectomy at a young age. It is thought that reduction of estrogen in the body brought on by oophorectomy can increase the risk of cardiovascular disease. In addition hysterectomy can sometimes lead to ovarian failure, which would have the same effect. This brings into question the safety and necessity of these procedures (oophorectomy in particular) as a method of treatment for endometriosis. It also brings into question the safety of some medical therapies for endo. Many of such therapies are based on the notion that reducing estrogen production in the body stops the endometriosis from growing. This can involve taking drugs that suppress ovarian production of estrogen, bringing on a menopause-like state. If indeed reduction in estrogen is linked to cardiovascular problems in women, then this form of medical treatment for endo could also be increasing the CHD risk this current study has observed. This paints a big neon sign pointing at the need for 1) more surgeons skilled at complete excision of endometriosis lesions and 2) the need for drugs that target endometriosis specifically and not have a whole body effect.

This study provides a good starting point for further work into endometriosis and CHD. In particular it would be interesting to see if increased CHD risk in women with endo is intrinsic (i.e. it is just something that comes along with endo) or modifiable (i.e. it is due to the aforementioned treatments). CHD is one of the biggest killers of women in the western world, so if the risk of CHD can be reduced in women with endo, then it is important for doctors, surgeons and drug companies to change their attitudes to how endometriosis should be treated.  


  1. You are very talented at relating to an avetage person on how to look at complex science studies for validity and meaning of statistical results for good interpretation. I really appreciate this.

  2. I really do wonder if the increase isn't also to do with unidentified lesions of the heart and lung, or as a side effect of synthetic hormone use that is known to give you a higher chance of blood clots