Tag Archives: stress

Four ways breast milk is really interesting

You might have heard a lot that breastfeeding may reduce the risk of infections, allergies and gut problems. But it’s perhaps even more fascinating than you realise.

1. Mums may produce different breast milk for sons and daughters

Dr Katie Hinde from Harvard University studies lactation in monkeys to understand how breast milk provides not only nutrition, but shapes immunity, nervous systems and behaviours in their offspring.

Her team has found that even a monkey mother’s own breast milk can vary in the composition of fat, hormones, protein and minerals. It can depend on her age, how many children she’s had and what she’s been eating now and in the past. But, as this Naked Scientists interview explains, it even matters whether she’s had a son or a daughter.

Rhesus macaque monkeys produce more, lower energy milk for daughters, but less, higher energy milk for sons, in such a way that the overall energy supplied balances out. Why this is is unclear and Dr Hinde’s team is working to unpick these tricky questions. The monkey mothers also produce more calcium for daughters, which Dr Hinde speculates is linked to a quicker development of daughters’ skeletons.

As the interviewer, Kate Lamble asks, how do the monkey mums know whether it’s a son or daughter? Dr Hinde thinks it’s probably down to more hormones produced during female foetal development affecting mammary glands. It could also be behavioural interactions between mother and offspring after birth.

The big question is, does this hold true for humans? Is this something that mattered more in our evolutionary past, but is less relevant in our cosier modern world?

2. Time of day matters

Many animals exhibit day-night rhythms that can affect everything from sleep-wake cycles, metabolism, immune responses and heart rate. And it seems breast milk production is no different.

Milk produced during the night contains higher levels of a hormone, melatonin, which is known to regulate day-night (“circadian”) cycles. Researchers have suggested this can help reduce irritability and prolong night-time sleep, but more work is needed to show this for sure. Adults can manufacture melatonin from essential molecules taken in through the diet, but babies can’t.

Other studies have focused on tryptophan – an important building block in the body’s biochemical manufacturing of melatonin. One study linked higher levels of tryptophan in breast milk at night with a rise in melatonin in the breast-fed babies, which was also associated with more sleep.

To try to establish whether elevated tryptophan caused improved sleep (rather than because of some other differences between breast- and formula-fed babies), another study compared babies who were fed formula milk with added tryptophan at night, added tryptophan in the day and with no added tryptophan at all. Only babies fed added tryptophan at night had better sleep and metabolites in the urine suggested this was down to the production of more melatonin.

Whilst the overall effect on babies’ sleep and whether fluctuations in the makeup of breast milk can really cause changes is still to be fully teased out, these findings suggest that mothers who express milk for their babies for a later time may want to pay attention to what time of the day they did it.

3. Hormones in breast milk can affect behaviour too

Hormone levels, such as cortisol, can naturally fluctuate throughout the day. Cortisol, in particular, is not only important in the stress response but is needed in the mammary glands to stimulate new milk production and protect the survival of mammary cells.

Researchers comparing breast- and formula-fed babies have suggested that higher cortisol levels in milk are associated with more fearful babies. Others studying monkeys and humans have reported levels of maternal cortisol affecting temperament in three-month olds, and this may differ for sons and daughters. For some animals, like red squirrels, it may give them a competitive advantage – cortisol-like hormone levels rise as a forest gets more crowded, which accelerates the growth of their offspring.

Back to Katie Hinde’s research. Again, studying rhesus macaques, her team wanted to know whether these effects were genuinely down to cortisol or because of variations in the amount of nutrients passed on (which are in turn affected by hormone levels). The researchers measured milk one month after birth, and again three to four months after birth. Generally, higher levels of cortisol in milk were associated with babies who scored higher for nervousness and lower for confidence.

But why? They point to evidence that elevated cortisol in humans may lead to reduced growth, and speculate that there may be a trade-off between infant temperament and growth – if more nervous, less confident behaviours reduce activity, then the available energy from milk can be put towards growth, particularly for sons. This may be particularly crucial in times when resources are scarce or competition is high.

At least in rodents, the receptors for these hormones are most abundant in the gut in infancy, before declining into adulthood. This suggests that babies of at least some animals may be taking an active role in sensing the environment through their mother’s milk.

 

4. Breast milk may shape the friendly gut bacteria

Californian researchers compared the bacteria in the intestines of breast- and bottle-fed baby macaque monkeys between five and 12 months old. They also took blood samples to analyse the immune cells in the growing babies.

The bacteria profiles in each group showed stark differences. The breast-fed babies contained higher levels of Prevotella, Ruminococcus and Lactobacillus, whilst the bottle-fed babies had higher levels of Clostridium. The immune systems of the two groups also differed. Breast-fed babies had more immune ‘memory cells’ and ‘helper cells’ (which help fight off foreign invaders) and produced a sturdier immune response when isolated blood cells were challenged. The researchers noticed differences in chemical signals in the blood known to influence how the immune system develops.

Another study, this time on mice, may give clues as to one way this can happen. By manipulating particular antibodies in maternal milk, these researchers showed that a lack of antibodies produced very different bacterial gut colonies and affected how well the mice could cope with an intestinal insult. Both studies showed that variations in bacterial profiles were still seen many months after the experimental diets ended, indicating that the effects on the immune system may be very long-lasting.

All this suggests that breast milk, possibly through the action of antibodies, causes certain helpful microbes to colonise the gut. These then produce a spectrum of chemicals that help shape the maturing immune system, making it better equipped to fend off infections and less likely to trigger allergic reactions.

The question is, for humans in today’s world, how much would these variations actually matter?

 

Looking after kids: it’s lovely but is it work?

Last week, I sent this tweet:

My wife had gone on a well-earned break for the day with a friend, leaving me in sole charge of our two-year old son and five-month old daughter.

We spent the morning around the house, slowly getting dressed, fed, washed and dressed again (we have a five-month old, remember). Finally, blessed with some gorgeous weather, we made it to the local park in the afternoon, before back for tea, bath and bed. Phew!

My point, squeezed into a snippy 140 characters, was in reaction to those who can be heard saying something like: “I put earplugs in/don’t do the night feeds/need lie-ins at the weekend (*recycle as appropriate) because I’m the one who has to go to work.”

I’ve certainly heard it. In my experience, always from men, many of whom I’m fond of and respect. I assume that when it is said, it’s usually from men, given the societal bias for women to take the extended parental leave, though I’m relying mostly on anecdote and supposition.

But, as I was changing the fourth nappy (diaper, my American friends) of the day with a two-year old playing ‘horsey’ on my back, I thought: “this feels on awful lot like work”. And at my office, I can make regular cups of tea, zone out for five minutes to check the news/Twitter and (usually) go the toilet when I want. I would like to see the bladder infection rates amongst parents, because I find myself ‘holding it in’ an awful lot.

From Men’s Health News

Don’t get me wrong, I had a lovely day and adore spending time with my kids. But it is hard graft.

Which is why this attitude really grates. My wife, who is currently on her second period of maternity leave, looks after the kids for the five working days, with our two-year old being at nursery school (preschool, my American friends) a couple of mornings the only partial respite. I did it for one day and felt the pinch.

But as Ian Curtis sang, routine bites hard. Day after day, going through those endless cycles of nappies, changes of clothes, feeding, shushing to sleep, is draining. And when you’re drained, doing it all over again sets up a tiring negative feedback loop.

This becomes even more acute when one considers that stress and lack of support can increase the risk of post-natal depression. Even without leading to such extreme consequences, it is beneficial for a child’s development for the parents to be less stressed. In fact, one study showed that minor daily hassles, which all mothers experienced regardless of background or family set-up, were related to more child behaviour problems, less satisfied parenting and poorer functional family status. The study also emphasised maternal emotional support, either from friends, communities or partners, as an important buffer from these adverse effects and to maintain mothers’ psychological well-being. I can’t even begin to imagine what it’s like to be a single parent, but find my anger rising as society moves to remove support for this group.

Again, I should say, we both get so much joy from looking after them and wouldn’t change them for the world. But it IS hard graft, and is why my wife’s break was more than fully earned.

Obviously, everyone’s situation is different. Many, many partners who ‘go to work’ are committed to helping a stay-at-home partner in the evenings and at weekends. Many people’s work is also incredibly demanding and stressful (more than mine), and this post is not a prescription of what ‘working’ parents ought to do, as it will depend hugely on circumstances.

But if you find yourself justifying an act with, “well I’m the one that works”, then you may want to have a second think.