Secrets of the Human Body. Andrew Cohen

immune system is still in its early stages, but Bruce thinks that the specific culturing of B. infantis, and the relative lack of diversity in the infant gut, may be crucial to the development of a mature immune system. In fact he is evangelical about this. He believes that the current epidemic of asthma, allergy and atopic disease in the US may be largely due to the loss of B. infantis from infant guts.

      B. infantis also seems to reduce intestinal permeability, tightening up the joins between cells. Leaking infant guts may cause sickness directly but also affect the long-term development of the immune system. Evidence for this comes from an extraordinary study in Bangladesh. The dominant species in the stools of the infants in the study was B. infantis and they were 96 per cent breast-fed. The more B. infantis in the stool, the more weight gain and the better the responses to oral polio, tuberculosis and tetanus vaccines.

      And there are the extraordinary little considerations that B. infantis makes in order to be a good houseguest. Other similar species of bacteria are not directly harmful but they do digest human mucus. When they do this they accidentally produce sugars that are useable by dangerous bacteria. By contrast B. infantis leaves the complex sugars in human mucus intact, starving the pathogens.

      Just as the early efforts to understand the link between breast feeding and infant health required collaborations between chemists, physicians and microbiologists to make remarkable progress, Bruce German has forged a multidisciplinary team at UC Davis. While Bruce was starting to dissect the chemistry of milk in the lab, neonatologist Mark Underwood, at the UC Davis children’s hospital, was treating and studying children born long before 37 weeks’ gestation. Over 10 per cent of children are born prematurely in the United States and they face a few singular challenges. Inadequate lung development is the most immediate problem, but in the weeks spent in intensive care after birth a devastating condition called necrotising enterocolitis, or NEC, claims many infant lives. In NEC the tissue of the gut becomes inflamed and dies, allowing the contents of the gut to leak into the abdomen, causing massive infection. It affects approaching 10 per cent of infants who are born weighing less than 1,500 g and half of those affected will die. In the decades he has spent caring for premature babies, the death rates from NEC have not changed significantly, but some clues that B. infantis may help to reduce this death rate are starting to emerge. Breast milk improves outcomes in NEC and additionally, a lack of Bifidobacteria seems to increase risk.

      Neonatal intensive care is a dangerous place to be. Paradoxically this may be because it is too clean, or perhaps clean in the wrong way. Antibiotics and continuous cleaning keep Bifidobacteria at bay, but disease-causing organisms flourish in even the most fastidiously clean units. A trial is just starting at UC Davis but the evidence from other studies shows that administering B. infantis as a probiotic (a dietary supplement containing live bacteria that promotes health benefits) together with human breast milk serving as a prebiotic (a dietary supplement to stimulate the growth or activity of commensal microbes), may help to further reduce the incidence of NEC.

      Bruce is enthusiastic about the use of probiotics even in term infants and suggested that I give my own child some B. infantis prebiotic. I asked why simply breast feeding wouldn’t be enough. ‘Because B. infantis is extinct in much of the developed world. It’s not a bacteria which acquires resistance easily and particularly in the USA the use of formula milk for multiple generations has simply starved it out of existence.’

      Bruce has the infectious enthusiasm required for truly visionary science but I wondered if I was being seduced by his ideas too easily. The genetic case was certainly persuasive that B. infantis had co-evolved with breast milk to be the main colonist of the infant gut. Why else would it have the entire genetic toolkit to use molecules found only in human breast milk, molecules which humans were totally unable to digest? But I wanted a clinical perspective so I asked Mark Underwood for his view. Mark is no less visionary than Bruce but he has the sort of quiet, clinical caution that comes from being a doctor in a speciality where a lot of child patients die. He was no less enthusiastic than Bruce. He believes the evidence stacks up from all sides and he is about to start a trial of giving B. infantis as a probiotic in the neonatal ICU. From the second week of life, I have been giving Lyra once-daily B. infantis supplements sent by Bruce.

      At the end of my conversation with Mark I asked if he himself had been breast-fed. ‘No,’ he replied. ‘Perhaps if I had been breast-fed I’d have been a surgeon.’ He was being ironic: surgeons may think of themselves as being at the top of the tree, but physicians like to joke amongst themselves that surgeons are mere technicians. But his answer contained an interesting truth. He was a healthy, successful person. It is true that the mother–infant pair are what Bruce calls a ‘powerful Darwinian engine’ driving extraordinary evolutionary change. Together they have co-opted another species as the world’s most effective nanny, supporting brain development and the development of the immune system, as well as fighting pathogens. And loss of B. infantis from our ecosystem may well explain the rise in allergic and atopic disease. But contained in Mark’s answer is the idea that, despite multiple generations of formula-feeding and antibiotics rendering this seemingly vital bacteria functionally extinct, it’s possible to become a healthy professor without it. People continue to live longer and longer. The human body has extraordinary resilience and redundancy; regaining B. infantis in our infant guts may well have wide-ranging benefits, but it is testament to our adaptability that we can survive without it.

      GROWING UP, UP, UP …

      When it comes to growing up, the van Kleef-Bolton family from London are world-class. At 6 ft 5 in (195 cm) and 7 ft (213 cm) respectively, Keisha and Wilco are the tallest couple in Great Britain and have only just been knocked off the global top spot, outranked by the lofty Chinese couple Sun Ming, 7 ft 8 in (233 cm), and Xu Yan, 6 ft 1 in (185 cm), in 2016.

      While Keisha and Wilco are outliers at the far end of the distribution of human height, collectively as a species we have all gone through an incredible growth spurt in the last 150 years or so. Since the middle of the nineteenth century records show that the average height in industrialised countries has increased by about 10 cm. That’s a serious increase in such a short space of time, and as far as we know it is unprecedented. In fact the study of early human skeletons strongly suggests that human height stayed pretty much the same from the Stone Age until the mid-part of the nineteenth century. So what happened around the 1820s? Well, all of the available evidence suggests that this swift increase in height was not driven by any rapid-fire evolutionary selective pressures. The time frame is far too short for evolution by natural selection to play out and there is no reason to think that height has been under particular selective pressure in the last 100 years or so. The environmental influences, on the other hand, seem to track very tightly with the increase in height. We know that if a child is malnourished or suffering from disease at particularly critical moments in childhood, they will never reach their full potential adult height. But since boys stop growing around their late teens and girls in their mid-teens, proper nutrition before puberty is essential to fulfil genetic potential for height. Protein, calcium, vitamins D and A all have an effect on height, and deficiency in all of these nutrients in the early nineteenth century was commonplace. But starting around the mid-1800s the punishing lives of populations through the early years of the industrial revolution began to give way to more widespread benefits, including better sanitation, clean running water and improved nutrition. Slowly this allowed the populations of countries like the UK to start fulfilling the genetic potential of human height. The truth is (as many parents instinctively know) that eating up your greens and drinking your milk really will make you grow up strong and tall.

      EAT YOUR GREENS PROTEINS

      During childhood the most important food that influences your final height is protein. Meat, fish, eggs, nuts, legumes and dairy products are all good sources of protein (which is why it is a considerable nutritional challenge to bring children up on a vegan diet). Other minerals, in particular calcium, and vitamins A and D also have a direct influence on height. For this reason malnutrition during the key stages of childhood can have a direct and significant effect on growth. This means good nutrition is particularly important before and around the growth spurts of puberty. For girls this begins around 10 years old and continues until their mid-teens when maximum