Why does breastfeeding reduce your lifetime risk of breast cancer?

[confusedfirsttimemum]

Please, please, please I don't want this to go like the other feeding and cancer thread. It's not knocking formula, it's not about feeding choices (or about feeding non-choices where support is poor). I have tried to word this thread title in as neutral a way as I can possibly come up with [Can you tell I'm a bit scared of a bunfight?]

So, disclaimer over.

Following on from that thread, a friend and I were discussing the stats about breastfeeding reducing a woman's lifetime risk of getting breast cancer. Does anyone know why this is believed to happen?

My friend thought it was probably to do with stopping ovulation, but in that case does the benefit cease when your periods come back? That didn't seem to tally with something I read saying that the longer you did it, the greater the protection. Most women I know got their periods back at some point between 6-12 months. Also, in that case why does the pill increase your risk slightly?

Sorry, I have tried googling but all I get is those breastfeeding promotion sheets. I am genuinely interested, in a nerdy type of way.

It seems obvious to me that hormones will affect the development of reproductive cancers. Physiologically, it's probably abnormal not to spend most of our adult life either lactating or pregnant. Stone-age woman started her periods at about 17 (because she wasn't as fat as we are!), and was either pregnant or lactating for the next 20 years. The !kung tribe in Africa are apparently the nearest thing to stone age peoples still in existence. The women suckle their babies and small children around the clock, and don't ovulate for several years after each pregnancy. I imagine they spend only a fraction of the time that we do menstruating - hence their hormonal profile is completely different in adult life.

We're simply not 'designed' to be menstruating as much as we are, or to live as long as we do after menopause - it doesn't surprise me at all that we have such a high rate of reproductive cancers in this country (most of which develop very late on in life).

"Most women I know got their periods back at some point between 6-12 months"

Sorry - wanted to add, that if we were thinner, and bf our babies dozens of times round the clock day and night, also introduced solids more slowly, our periods wouldn't probably come back so quickly after childbirth.

Most babies would suckle dozens and dozens of times a day if we were carrying them around in our arms all the time against our breasts (as stoneage woman must have done). Even mothers in the West who think they're bf on demand probably don't bf anything like as much as our forbears did.

Yes, but I suppose what I'm interested in is what hormonal aspect of breastfeeding is believed to give the protection.

For example, I breastfed on demand, but by periods came back about 7 months. DD is now one, does that mean that I no longer get any protection from breastfeeding, or is it believed to be some other hormonal change? That's what I'm getting at. [Not that it affects my feeding decisions, just a nerdy interest]

Sorry, cross post on the demand feeding. I assume that the research on breast cancer reduction must have been done on modern women though, so it must be that profile that tells us where the benefit comes from?

I think it's the reduction in exposure to oestrogen in lactating mothers that might be implicated in lower risk of reproductive cancers. Wouldn't put my life savings on it though!

I thought it was also to do with the breast tissue 'maturing' (for want of a better word) during pg and then being 'used' to bfed.

If you never get/stay pg your breast tissue would stay at post pubertal growth level and never reach mature breast tissue state. I think that the required gestation mentioned on my peer supporter course for being able to induce lactation was 20 weeks (i.e. reaching mature breast tissue state).

I may be completely wrong on this front though

It is interesting.
It makes me want to have about 6 more children, as well

however there are other types of cancer that are encouraged by childbearing, it would seem - skin cancer for example is thought to be possibly aggravated by pregnancy.

You can't win, really.

btw if of interest to anyone, ds2 was 28 months when I started ovulating

he was still largely breastfed. (still trying to wean the bugger, he's nearly 3)

Just off the top of my hesd - for a similar reason that men who don't have much sex or masturbate much are at higher risk of testicle cancer? You have a body part meant to do a job, if it doesn't get the chance to, it's more likely to malfunction.

Meant to be head, not hesd.

Not to worry, confused - many of us here enjoy a good nerdy, non-confrontational debate I believe the most widely accepted reason why breastfeeding protects against breast cancer is that it reduces your exposure to oestrogen, which 'fuels' breast cancer (don't ask me how this works!). There are other factors, some less well understood.

I honestly don't know about the link with ovulation, but what I think you're asking here is about how long the protective effect lasts - ie, is it limited to the early months of breastfeeding, does it stop when your periods come back?

The answer to that question is No - it's the total duration of breastfeeding across all your children that counts. Statistically, breastfeeding one child for two years gives the same protection as breastfeeding four children for six months each. The second year of feeding a child is therefore just as protective against breast cancer as the first, so the longer you breastfeed every child the more you lower your risk.

The evidence here comes from this study which is the most comprehensive piece of evidence to date confirming the protective effect of breastfeeding. This analysis of the study says that "The reduction in relative risk was 4% for every 12 months of breastfeeding over a woman's lifetime, and this result was the same irrespective of a woman's parity" - ie, it didn't matter how many children she had, it was the total duration of breastfeeding across all of them that counted. (Caveat: pregnancy itself is also protective, so having more children reduces your risk still further - but this doesn't change any of the above).

Hope this makes sense - and happy to be corrected by folks that know better!!

Then surely those who take hormonal contraception should have fewer cancers, as they have lower oestrogen - especially if they have progesterone only protection, oestrogen production being suppressed, with no ovulation?

This has been puzzling me too: I had thought it was also something to do with the actual production of milk in the glands stopped them calcifying - which is what a tumour is, rather than just wholly an oestrogen suppression event.

And maybe we are more aware of our breasts when and after b/f so we are more aware of any changes, and we get them checked out and earlier.

Not wanting to inflame anyone, but do we have better nutrition if we are the type of person who b/f - attachment parenting / knit our own yoghurt, weave our own yurt types?

Would better nutrition - including more nutrients from whole and raw foods be part of the picture and profile of a b/f woman?

Would this nutritional profile influence the figures of breast cancers as a factor, independent, per se of actual baby feeding methods?

It is more complicated than just oestrogen - there are various factors involved, both with breastfeeding and with the contraceptive pill. And "cancers" is not the same as "breast cancer"!

Remember that the study above simply points to the extremely clear correlation between breastfeeding and reduced breast cancer. It doesn't give any physiological explanation as to why this is so, but it does remove every other possible causative factor you can think of, so we know that the effect is due to breastfeeding and not something else (e.g. nutrition, breast awareness etc).

That's so interesting, thanks guys. Looking at the study boobmeister it says that there is no difference in reduction of risk between developed and developing countries. Now taking a bit of a leap, since those in developing countries do seem to feed more frequently, and that's what delays ovulation, it does seem to suggest it's a complex pattern doesn't it?

Thanks everyone. I've just made it to a year of feeding DD, and no plans to stop any time soon. Nice to have a little feel-good point to ponder.

Those in developing countries don't necessarily feed more frequently - e.g. babies in African agrarian societies might spend most of the day on their big sister's back and be taken to their mum to feed every few hours while she is working in the fields. Other societies are different to ours in different ways!

But thank you too - you have made my Monday morning most interesting too!

True. I suppose I phrased that badly. I suppose what I meant to say is that, across the world there are different feeding cultures in different areas. The fact that that location/society didn't seem to make a difference to the reduced risk of breast cancer seems to suggest it's something fundamental about feeding, not just feeding so much you don't ovulate.