Tag Archives: microbiome

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?

 

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Parenting science: 12 top stories of 2012

It’s that time of year when we’re flooded with ‘best of’ lists, so allow me to jump on the bandwagon. 2012 has been a great year for science – the discovery of the Higgs Boson, the landing of Curiosity rover on Mars, and the ‘encyclopaedia of DNA’ that has given us the deepest insights into the human genome.

Here, I’ve picked out some of the stories that might interest parents, covering areas such as child learning and development, reproductive technologies, embryology, genetics, and even a bit of public policy thrown in. I’m sure I’ve missed some interesting ones too, so please add yours in the comments!

Mouse eggs created from stem cells for the first time (New Scientist)

Once a fully functional body cell develops from a ‘parent’ stem cell, it’s thought there is no going back to the previous state. A team of scientists in Japan, however, used a cocktail of signalling molecules to reprogram skin cells to become immature egg cells in mice (they had already done this to create sperm cells). What’s more, these cells could be fertilised and, in some cases, led to healthy mouse pups. This was a stunning feat of biological engineering that will help in the study of mammalian development and also hold promise in treatment of infertility. In a related story, controversy over whether biology textbooks need to be re-written took a turn when more convincing evidence was published that the number of eggs in a female isn’t fixed for her lifetime but can instead by replenished from a stem cell stock.

‘Chimera’ monkeys created in lab by combining several embryos into one (The Guardian)

The headline is pretty self-explanatory and the article itself is a fascinating read, so I won’t re-invent Ian Sample’s superbly crafted wheel. So if you want to know more about the controversial technique of creating normal, healthy monkeys with cells from more than one embryo and why it might benefit stem cell therapies, go read it! This may not be as bizarre and ‘unnatural’ as it first sounds, though, as we may all be walking chimeras and carry cells from siblings, aunts and uncles.

Genome Sequencing for Foetuses (Wired Science)

Being able to test foetuses for genetic faults that increase the risk of a serious disease, such as Down’s syndrome and blood or nervous system disorders, is hugely important. This is currently done mostly by invasive techniques such as taking samples of the placental tissue or amniotic fluid. This study, however, showed that it’s possible to work out the foetus’ genetic make-up by piecing together tiny fragments of DNA floating around in the mother’s blood. The ease of such a test would, of course, raise ethical issues about what is appropriate to screen for and what counselling parents would need, as well as requiring a firm and clear communication of risk.

DNA-swap technology almost ready for fertility clinic (Nature News)

Mitochondria are little energy powerhouses within most of our cells and they contain a small amount of their own DNA that is inherited wholly from the mother. A range of devastating diseases, that can affect the brain, liver, muscle and many other organs, are caused by defects in this mitochondrial DNA. A group of US researchers showed it was able to swap the mitochondria in a mother’s egg with one from a healthy donor to produce a normal looking embryo free from the mitochondrial genetic faults (restrictions on this technology would not allow a live birth). You can read about how the scientists actually did this in David Cyranoski’s article. And I would add that, contrary to some scare stories, these would not be ‘3 parent babies’ – mitochondrial DNA contains only 37 genes (involved in protein synthesis and biochemical reactions that make up respiration) compared with the many thousands of genes coded for by the DNA in the nuclei of our cells.

Babies are born dirty, with a gutful of bacteria (New Scientist)

Earlier this year I blogged about the “The microworld that lives inside you” and how the microorganisms that outnumber our own cells 10:1 are first transmitted from mum as a baby is born. A study by Spanish scientists, suggested that this isn’t the whole story. By studying the “meconium” – the baby’s first poo that is made up of materials ingested during the time in the womb – they detected two types of well developed bacteria. We don’t know for sure, but these were probably passed from the mother through the placenta. Our so-called “microbiome” is really important, because it influences our digestion, immune system, risk of disease, and maybe even our personalities.

Childhood stimulation key to brain development, study finds (The Guardian)

A US study provided more evidence that a sensitive period of learning and development exists early in childhood. They surveyed children from when they were four years old, recording details such as the number of books and the types of toys they had, to measure the amount of mental stimulation to which they were exposed. They also scanned the brains of the same children when they were between 17 and 19. As Alok Jha explains: “…the more mental stimulation a child gets around the age of four, the more developed the parts of their brains dedicated to language and cognition will be in the decades ahead.” Of course, this was an observational study and so limits the strength of the conclusions about whether the types of toys really caused brain developments, but the way the researchers tracked the same children over many years and the factors they took into account (parental nurturance had little effect, for example), was particularly impressive. Another cautionary note: the results were presented at a scientific conference and, as far as I know, have not appeared in a scientific journal, which means it won’t have yet been properly quality assessed by experts.

Golden ratio discovered in uterus (The Guardian)

At the risk of straying into mysticism, this was a nevertheless alluring report of a Belgian gynaecologist’s claim that the uterus represents an aesthetically pleasing “golden ratio”. This ratio is derived from something called the “Fibonacci sequence”, which is a sequence of numbers starting 0,1,… where every subsequent number is the sum of the previous two (so: 0, 1, 1, 2 , 3, 5, 8, 13, 21,…). The ratio between pairs of number in the sequence (divide one by the other) ends up being 1.618, which is the “golden ratio”. As Alex Bellos explains, its devotees believe it expresses aesthetic perfection and is found wherever there is beauty. According to Dr Verguts, when women are between the ages of 16 and 20 and at their most fertile, the ratio of uterine length to width is 1.6, spookily close to the “golden ratio”.

What happens to women denied abortions? This is the first scientific study to find out (io9)

Another set of results presented at a scientific conference, rather than in a scientific journal, but that is worth noting nonetheless. Annalee Newitz cites a Facebook post written by the lead researchers of a study that followed up women who had sought abortions at different abortion clinics in the US: “We have found that there are no mental health consequences of abortion compared to carrying an unwanted pregnancy to term. There are other interesting findings: even later abortion is safer than childbirth and women who carried an unwanted pregnancy to term are three times more likely than women who receive an abortion to be below the poverty level two years later.” Newitz further emphasises the preliminary results: “When a woman is denied the abortion she wants, she is statistically more likely to wind up unemployed, on public assistance, and below the poverty line.” If these findings turn out to be valid when further quality checks are carried out, they could help shape the debate on abortion policies and the state support a women seeking an abortion receives.

Boys and girls may be entering puberty younger (New York Times and The Guardian)

A study on the timing of puberty in boys by the American Academy of Pediatrics complements an earlier study on girls, which both hinted that puberty is, on average, starting gradually earlier in both sexes. Current estimates, at least for US children, are that the average age of puberty onset is around 9 years in black boys and girls and around 10 years in white boys and girls (although full sexual maturity may happen later than this). No one, as yet, knows why, but speculations include diet, changes in physical activity, improvements in healthcare, and chemicals present in the environment that affect our hormones.

Fathers bequeath more mutations as they age (Nature News)

A Swedish study concluded that a father passes on more genetic mistakes to their children than do mothers, and the older the man, the more mutations he is likely to pass on. This is most probably explained by the fact that sperm are generated from dividing ‘precursor’ cells throughout a man’s life and this cell division becomes less precise with age. Most inherited mutations won’t lead to any problems for the child, but the occasional one may increase the risk of a genetic disease like autism or schizophrenia. Taken together with rising average age of fatherhood, does this help explain, at least in some part, why autism rates are rising? (It could, but awareness and diagnostic changes are also likely to be at play). It’s not definitive and it shouldn’t scare older would-be fathers, but it may help in better informed decision-making.

An HPV Vaccine Myth Debunked (New York Times)

One of the arguments opposing vaccinating children against the Human Papilloma Virus (HPV), which can cause warts and cancer, is that in the minds of the young girls it frees them up to be sexually more promiscuous. Studying long-term medical data from girls in Atlanta, USA, however, showed no difference between vaccinated and non-vaccinated girls in pregnancies, sexually transmitted diseases, testing for sexually transmitted diseases, or contraceptive counselling. The article finishes by saying: “As one expert said, parents should think of the vaccine as they would a bicycle helmet; it is protection, not an invitation to risky behavior.”

Hungry mothers give birth to more daughters (Nature News)

Another eye-catching story was the report that during the Chinese Great Leap Forward famine, the proportion of boys being born dropped (from 109 boys for every 100 girls to 104 boys for every 100 girls). This sets up the tantalising possibility that sex ratios are adjusted in response to environmental conditions such as nourishment, a situation already known in deer where undernourished males tend to have fewer offspring than undernourished females (although in humans other factors like psychological and physical stress could be at play).

A final story that caught my eye was the latest results from the Avon Longitudinal Study of Parents and Children (ALSPAC), also known as the Children of the 90s, which probably warrants a blog post in itself. Nature News covered it and The Guardian’s sublime Science Weekly podcast featured it too (after 26:10). My favourite bit was how they collected the children’s milk teeth: “We had to negotiate for those. They are worth money to children, after all. In the end, we only got the milk teeth when we presented each boy and girl with an official Alspac form, signed by the tooth fairy.”

How sweet!

The microworld that lives in you

From a pod near you

I love a podcast. Episodes of audio goodness are delivered daily or weekly to my MP3 player, ready to keep me company on my long commute. I subscribe to podgrams dealing in current affairs, football, history and comedy.

But the overwhelming amount of disk space is taken up by science. Scientific news, scientific scepticism, scientific ideas, science in culture and scientific history. Even science comedy. Science science science.

Sometimes issues related to pregnancy and childbirth, childhood and parenting crop up, which as a science-minded parent is right up my street. And, I hope, right up other people’s streets too.

Here are some nuggets with which to start.

Ed Yong on BBC Radio 4’s Four Thought | 19 Oct 2011

Science writer Ed Yong describes his fascination with the human ‘microbiome’ – the bloom of microbes that each of us house in and on our body. The cells of bacteria, fungi and other microorganisms actually outnumber the cells of the human host by 10 to 1, and their genes by 100 to 1. Are we humans hosting a microbial community or a superorganism in which human cells are simply partners?

We can’t function as we do without these microbes. They help to digest complex foods like carbohydrates, metabolise drugs and toxins, interact with our immune system, and affect energy balance. The types and numbers of microbes within each of us are different and can depend on diet, environment and behaviour. The microbiome may have even played a part in shaping our evolution. They have such an important role that the microbiome has been called the ‘forgotten organ’ or the ‘second genome’. How, then, would you define what is ‘us’ – is it any cell that contains the same DNA as when we were an embryo, or are the constantly interacting microorganisms that are vital to our survival ‘part of us’.

What’s really interesting, at least from someone interested in child development, is how we gain this microworld. As Ed explains in the audio clip, we develop in the sterile environment of our mother’s womb*. The first gift from our mum is a smattering of microorganisms, but this depends on how we are born. A baby born of a vaginal birth is delivered their birthday presents as they travel through the vaginal canal and slides past (brace yourselves) the mother’s anus. The makeup of bacteria in vagina of pregnant women is actually quite different from that in non-pregnant women. A particular bacterium, usually found in the gut where it helps digest milk, becomes far more abundant in the vagina during pregnancy, which may give the baby a healthy coating as it is born.

Babies born of a caesarian section, however, do not have this close encounter and instead pick up a different spectrum of bugs that more closely resemble the ones found on skin. It can then take a while for the full complement of gut bacteria to establish.

The community expands and becomes more varied as the child interacts with its surroundings. Breast milk has been found to contain up to 600 species of bacteria, which furnish the babies gut and hinder the growth of any harmful nasties. Babies are then ready to take in more complex foods. This in turn fosters a richer microsociety and the mutual relationship continues. Environmental contaminants and toxins can perturbe the microbial community, which has been suggested (though not proven) to contribute to type II diabetes, cardiovascular disease or obesity.

Kerri Smith on Nature Podcast | 23 August 2012

Kerri Smith on the Nature Podcast reports on recent research that shows how antibiotics, at least in mice, can affect the gut bacteria composition and, consequently, the amount of body fat. The antibiotics seem to spur the bacteria into producing more fatty acids, which are converted by the human host into fatty tissue. Listen from 05:45 – 11:35 to hear a discussion with one of the researchers on the study of antibiotics in early life and the possible link to obesity.

And another fascinating potential of our microbiome is discussed by Chris Smith on The Naked Scientists podcast. Listen from 16:30 – 20:55 to hear Dr Marcello Riggio talk about how certain bacteria can promote oral health (good!) but also lead to bad breath or tooth decay (bad). Skip to 21:00 to hear a debate with Prof Gareth Morgan on whether probiotics – beneficial bacteria supplemented in the diet – may help to prevent/treat allergies and gut infections by interacting with the host’s immune system (ends 26:30). This idea is, however, not fully supported by the current evidence: results are variable and inconsistent (see The Cochrane Library reviews on allergies, eczema, colitis and diarrhoea).

Chris Smith on The Naked Scientists | 5th Sep 2011

Click to listen to: The_Naked_Scientists_in_Africa

And, finally, an even more fascinating potential of our microbiome is discussed by Mo Costandi in his Neurophilosophy blog. The bacteria in our guts may have the ability to affect brain development and mood.

For more on the wonder of the microbiome, read Ed Yong’s excellent blog post and Carl Zimmer’s article in the NY Times.

*or, maybe not.

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