Tag Archives: sleep

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?


On the social environment

I was brought to thinking about child development and the influence of early parental nurturing after watching a lively exchange on BBC’s Newsnight between the clinical psychologist, Oliver James, and Dr Ellie Lee, a lecturer in social policy at the University of Kent.*

From what I could see, the intense antagonism (aside from James’ unwavering dogmatism) was partly the result of a difference between a purely clinical look at child development, by which controlled scientific studies are held up to encourage the need for early intervention, and the sociological implementation of these ideas, which can introduce many variables to successful intervention.

For instance, showing that supportive parenting behaviours can lead to improved mental and language abilities in infants is one thing (as James would point out), but how you successfully communicate that to parents and change behaviour, is another (as Lee might counter). To lay down a hard-and-fast prescription for parents to follow, without layering burden upon burden, is not always straightforward. A more nuanced approach is required, as appreciated in the Early Intervention report featured in the Newsnight item.

Oliver James, in particular, seems very disposed to attach blame to a parent for any perceived character flaw in their child, and guilt-tripping parents in this way seems an overly blunt approach. And this is the point that Dr Lee may have wished to explain more explicitly.

It seems to me, albeit speculatively, that the parent’s well-being is an important consideration when encouraging them to follow particular regimens. The current consensus of the scientific community may be that a child should be doing X, Y and Z, but it may also be the case that to achieve this, one or both of the parents would end up dangerously sleep deprived, mentally exhausted and with a strain on their relationship. This would be differentially affected by a person’s physiology, underlying immunity, predisposition to mental illness, and so on. It would also depend fairly heavily on a person’s life – their age, whether they’re a single parent, in proximity to close family, in a high pressured job, etc. All of these considerations temper any absolute assertion of an intervention based on clinical data.

The field of psychosocial research, which seeks to understand the interplay between one’s psychology and their social environment, is an important factor to consider when establishing any health initiative. It would be great to see whether there is any direct evidence related to this in the context of early intervention programmes for parents. A recent special issue in the journal Science, lays out some of the issues facing educational intervention initiatives, including the obstacles faced when moving from scientific research to public policy. The need for a holistic approach is summarised in the introduction:

Early childhood education remains peppered with both opportunities and debate. Continued progress will require new research that bridges traditional disciplines of neuroscience, psychology, sociology, economics, public policy, health, and education.

So whilst the clinical research may show that a particular intervention leads to the absolute best outcomes, it may be that a parent ends up finding a middle ground that still provides a beneficial environment for their child, but also a satisfactory outcome for themselves (a sort of cost-benefit assessment, if you like). It would be no good hectoring parents into following a specific course of action, with no amount of flexibility, if it leads to a significant worsening of their own physical or mental health, especially if the knock-on effect is a deterioration in family relationships. It seems highly unlikely that this would allow people to be good parents nor provide a decent environment for the child (a brief look at the scientific literature suggests this assumption isn’t entirely unreasonable, e.g. this, this and this).

I should emphasise that I do not wish to appear as though I am justifying or accepting of ‘bad behaviour’ of parents. There are clearly things we should all strive to do, things that are a struggle, and this will involve a series of adaptations, compromises and sacrifices.

Why, say, do one in five British adults smoke when we know categorically that is causes lung cancer, heart disease and increased risk of stroke? Worse, why do so many adults still smoke in the presence of children or during pregnancy, when passive smoking can cause the same health problems in children (and more) and parental smoking increases the chances that a child will smoke as an adult? A look at how mothers from disadvantaged backgrounds respond to tobacco control initiatives gives some clues – in short, increasing stigmatisation can be counter-productive.

I would like to think, though, that most, if not all, parents are happy to put their very best efforts in and would never be wilfully neglectful. But the point which seems to emerge is that the results of clinical research should be considered against a backdrop of social and population variances. In the case of early intervention, labelling a child as ‘at risk’ or categorically predicting their development, could be helpful in targeting the right guidance and support to the right people, but should not lead to undue and counter-productive stigmatisation.

So, appreciating that each baby, each parent, each family’s circumstance is different, is very valuable. It is critical, as always, to be guided by the scientific evidence available and make this the basis of any initiative to improve child development, but it may not be possible to then arrive at a ‘one-size-fits-all’ formula, a point similar to that made by Dr Luisa Dillner regarding sleep routine.

In short, it’s complicated. Plus ça change…


* Better quality video embedded (05/10/2011) – thanks to Denys Andrianjafy.

I feel like a pigeon…

Photo courtesy of thierr26.free.fr (under Creative Commons licence: http://creativecommons.org/licenses/by-nc-sa/2.5/)

One of the famous tests by behavioural psychologist B.F. Skinner was an experiment in which food was presented to hungry pigeons at pre-determined intervals. The pigeons in the experiment would then associate whichever random behaviour they happened to be performing at the time (e.g. pecking at a particular spot, nodding its head, walking in a circle, etc.) with the appearance of the food, and a type of learning called operant conditioning would take place.

Each pigeon would keep displaying the random behaviour until the food re-appeared, thereby reinforcing the association and strengthening the false association between cause and effect. This was interpreted by Skinner as the pigeons showing ‘superstitious’ behaviour. In fact, as demonstrated on illusionist Derren Brown’s TV programme, this seems to work in humans too.

So why am I writing about pigeons? Well, I feel like I’m experiencing my own version of this superstitious behaviour with our little boy. It’s probably fair to say that he’s at the lower end of the bell curve of hours of sleep per day, given the average of around 16 hours a day. So we find ourselves having to do a lot of soothing between his unerringly regular feeds.

This means we’ve taken to all sorts random behaviours, from sitting him in a particular chair to playing Bach DVDs. Sometimes one of these will work and we then become convinced that that is what he needs to lull him to sleep.

It’s also very tempting to start to draw conclusions about what he does and doesn’t like on a higher emotional level, especially when a smile or a fixated stare coincides with a stimulus. It seems that early newborn smiling does not necessarily carry any emotional content and is rather a spontaneous event for up to at least one month. Their vision also has a long way to go in development. Any stimulus that co-occurs with such a behaviour can easily be causally linked in the observer’s mind, which obviously has implications for the emotional state projected upon the infant.

Clearly, social smiling and cognitive awareness do start to develop within the first few months of a baby’s life, but I thought I’d make this cautionary note on an intriguing behavioural trait that we all exhibit from time to time.

And it may be the case that walking sends my son to sleep, but I can’t help feeling like a pigeon when I’m on my third lap of the block.