Dear Science,
WTF is the difference between hormone replacement therapy and birth control pills? Why is hormone replacement therapy considered so horrible and cancer-causing while birth control pills are not?
Waiting For My Annual Exam
Your question is an astute one. The hormones in birth control pills and in hormone replacement therapy are (roughly) the same: a mix of progesterone and estrogen. Here’s the truth: There is actually almost no difference in absolute risk between being on the pill and being on hormone replacement therapy. What differs is the perception of the risk.
Ovulation, objectively, is an unwise idea for your health. Unmolested, the female reproductive cycle involves a crescendo and decrescendo of estrogen followed by a peak and crash of progesterone each month. With the rise and fall of estrogen, tissues in the breast, the endometrium, and the ovaries are stimulated to grow, divide, and then die off. All of this brisk growth and destruction—as you’d expect—adds up to a risk of cancer later in life. The more cycles, the bigger the risk of cancer in the reproductive system—generally the big cancers for women.
Stopping this cycling is the key to reducing the risk—having lots of pregnancies or staying on the oral contraceptive pill (which hormonally mimics pregnancy). Menopause stops all this cycling—resulting in low levels of both progesterone and estrogen—and ends the accumulation of risk.
Hormone replacement therapy started as a means of smoothing out the chaotic estrogen and progesterone levels that cause the symptoms at the start of menopause: About half of women experience sleep disturbances, one-third experience mood disturbances, and up to 80 percent experience hot flashes.
A huge study was undertaken to learn about the effects of hormone replacement therapy: the Women’s Health Initiative. With hormone therapy, in the WHI study, came increased risk of heart attack, stroke, and invasive breast cancer. For example, 37 out of 10,000 women receiving the hormone had a heart attack, as compared to 30 out of 10,000 not receiving the hormone.
There are two ways to think about this risk. As a relative increase, this represents a 23 percent increase (sounds scary). In absolute terms, seven out of 10,000 women had heart attacks they wouldn’t have had if not started on hormones. That’s a much less scary way of looking at the same results. On hormones or not, the risk is small in absolute terms—higher on hormones, but still small. Similarly, being on the pill slightly increases your chances of a heart attack, stroke, or blood clot (particularly if you are a smoker). The chances are similarly tiny—on the contraceptive pill or not. We don’t worry about the pill, because we’re more rationally considering the absolute risk—increasing the chance of a very unlikely bad thing really isn’t that big of a deal overall.
Riskily yours,
Science
Send your science questions to dearscience@thestranger.com.
Don’t forget that on the pill, a woman has one less risk factor — pregnancy. While small, there is a risk of death from pregnancy, a risk that is virtually gone when on the pill. Last time I looked (10-15 years ago?), the actual death rate was slightly lower when on the pill. Or so at least my memory tells me.
Jonathan,
37 vs 30 heart attacks, that’s just about down in the statistical noise. If the true average number (say, if you did the study with 1,000,000 subjects, instead of 10,000 in order to get a really precise average) were 36 out of every 10,000, and if you took two samples of 10,000, and treated one with green placebo pills and one with red placebo pills, you’d expect the GreenHeatAttacks-RedHeartAttacks to be either greater than 8 or less than -8 about 1/3 of the time. In this particular study, a difference of 7, even less extreme than a difference of 8, has very little statistical significance. If that’s the most decisive study that’s been done on the connection to heart attacks, then there’s an excellent chance that HRT has no effect on the incidence of heart attacks. (Especially if there is no prior reason to expect a connection one way or the other.) This is especially true if they did the study and looked for differences in the incidence in many different diseases.
But I’ve tweaked you about related topics before. And to be fair, the main point of your post is that the additional heart attack risk fron HRT is small, not whether it might actually be vanishing (or, who knows, negative!)
Is the connection to invasive breast cancer or stroke any stronger, statistically speaking? I had read in the papers about the myriadd risks of HRT, but if this heart attack effect is as strong as it gets, statistically speaking, I feel misled.
When I’m Emperor of the Universe, no science journalist will be able to practice his or her trade until they’ve enrolled in (and received a passing grade in) the Eric from Boulder Workshop on Statistics for Science Journalists. Until I seize the imperial scepter, I’ll content myself with sniping impotently on SLOG.
Later research has demonstrated fairly conclusively that WHEN a woman begins hormone replacement therapy matters a great deal. A woman who begins fairly young (e.g. 50s) is much less susceptible to negative effects than a woman who begins her 60s or later. The study you cite was criticized for having too many older subjects and offering essentially useless guidance to women in their 50s.
There is a huge difference between hormone therapy and BIO-IDENTICAL hormone therapy. If it’s done right women replace their hormones by the phases of the moon, using dosed amounts on the skin. The pill is not a good method of birth control if you ever want to have children later on, because it kills off your best eggs. Read the book Sex, Lies and Menopause by T. S. Wiley
I am old enough to have seen both myself and my female friends go on the pill (or not), and take HRT or not. In the group of about 20 women I knew in high school and remained in touch with, 5 have died of breast cancer, and 7 are breast cancer survivors. That is far too many. Admittedly, we were the first generation of women to have access to HRT, and the doses were much higher then, but I wouldn’t advise anyone to do it.
I never did HRT myself, and used birth control pills only briefly. I am one of the lucky ones.
I am old enough to have seen both myself and my female friends go on the pill (or not), and take HRT or not. In the group of about 20 women I knew in high school and remained in touch with, 5 have died of breast cancer, and 7 are breast cancer survivors. That is far too many. Admittedly, we were the first generation of women to have access to HRT, and the doses were much higher then, but I wouldn’t advise anyone to do it.
I never did HRT myself, and used birth control pills only briefly. I am one of the lucky ones.
Karin your best eggs die off first period. Whether you bleed them out or they get absorbed into your tubes or uterus is really just a matter of the former being less pleasant than the latter.
This is why having babies at an older age is more risky-the eggs are more likely to have DNA errors and other problems. Birth control doesn’t exacerbate that fact.