Mother's milk isn't just for babies anymore.

Global chemical giants DowDuPont and BASF SE are investing millions to ramp up production of an indigestible sugar found naturally in breast milk.

Infant formula makers like Nestle SA can't get enough of the synthetic ingredient. Now the companies are eyeing a potentially bigger customer: adults.

DuPont estimates the annual market could reach $1 billion.

Human milk oligosaccharide is the third most common solid in breast milk, after lactose and fat.

HMO escapes digestion, allowing it to reach the colon where it feeds beneficial bacteria. HMOs may explain why breast-fed babies tend to fare better than formula-fed, said Rachael Buck, who leads HMO research at Similac formula-maker Abbott Laboratories.

"It's just been a fascinating treasure trove of benefits that we've uncovered,'' Buck said.

In babies, HMOs strengthen the developing immune system, helping fight infection and inflammation while aiding brain development, according to early research. New studies show those benefits may extend to people of all ages, fitting neatly into consumers' growing fascination with probiotics - the "good" bacteria that can help keep a human body healthy.

Replicating Nature

Synthetic HMOs come from the formula industry's quest to manufacture a breast-milk substitute that's as close to the real thing as possible. The purported benefits are still viewed with skepticism by some in the scientific community - especially when they come at a premium price.

"Never assume that the addition of a component of human milk actually makes the formula like human milk,'' said Steven A. Abrams, chair of the American Academy of Pediatrics committee on nutrition. "It's not," said Abrams, a Dell Medical School professor at the University of Texas at Austin.

HMOs could lead to treatments for adult ailments such as irritable bowel syndrome, allergies and even the ageing brain, Buck said. An animal study at Abbott's labs showed that HMO stimulated the vagus nerve, "a superhighway communicating from gut to brain," she said. "This has the potential to help both brain development early in life and, later in life, brain decline."

Commercial production is typically accomplished through a fermentation process using giant vats filled with microbes genetically engineered to produce specific HMO varieties, such as 2'FL.

DuPont plans to spend $40 million building out its HMO production capacity this year, its second biggest capital investment after expanding a factory that makes Tyvek. Meanwhile, it's partnering with Lonza Group AG to make enough product to meet current demand. DuPont will become a stand-alone company when it splits from DowDuPont on June 1.

After two decades of research, Abbott was first to bring HMOs to the US baby nutrition market in 2016. It's now expanded to 15 countries. Nestle last year rolled out HMO formula in Gerber and other brands across 40 countries. HMOs nourish bacteria that "train'' immune system cells, 80% of which reside in the gut, said Jose Saavedra, Nestle chief medical officer.

The health claims propelled about $600 million in sales of HMO formula last year for each of Abbott and Nestle SA.

Among Abbott's customers was Heidi Haydock, a senior manager at Cardinal Health, who two years ago wasn't able to breast feed her newborn son because she was undergoing chemotherapy for breast cancer. Concerned about the development of his digestive system, she fed him Similac with HMO.

Next Best

"With a mom who can't give breast milk, you kind of feel deficient,'' Haydock said. "Being able to give the next best alternative made me feel better.''

While some research indicates advantages to HMO-enhanced formula, it's not clear that there's a long-term health difference, Abrams said. In the US, babies fed generic formulas, which are as much as 50% cheaper, have outcomes "every bit as good'' as those fed pricier formulas, Abrams said.

Even in nature, breast milk can vary depending on the different kinds of sugars produced by each mom. DuPont and BASF are focusing on making the most common version of HMO, which consists of the 2'FL sugar. That's where the benefits can be seen most clearly, according to Nestle's Saavedra: Babies getting 2'FL from their mothers have slightly lower rates of acute infection than babies whose moms are deficient in that HMO.

Widening Market

BASF began scaling up production of 2'FL earlier this year, and it's studying how the different health effects of HMOs might be developed into a range of products beyond baby formula.

"Our aim is to expand on our scientific know-how on specific health functions of HMOs to adults as well," said Stefan Ruedenauer, BASF director of human nutrition research and development. "BASF will have a pipeline of science-driven products with substantial health benefits of HMOs in the near future."

Smaller rivals making the ingredient include closely held Jennewein Biotechnologie GmbH and FrieslandCampina of Germany.

Danish biotechnology company Glycom S/A is targeting the adult digestive health market with HMO supplements it began selling in the US and Europe late last year. The company touts its Holigos IBS product as managing symptoms of irritable bowel syndrome, including abdominal pain, constipation diarrhea and bloating. It sells 28 doses on Amazon.com for $50.

Probiotics Craze

HMO is just one part of DuPont's larger foray into digestive health, a loosely regulated market growing 20 percent a year. The company sees an estimated $5 billion annual opportunity developing gut-health products, though some experts question whether the supplements benefit everyone. DuPont is already a leader in probiotics, offering the widest variety of strains and operating the world's largest probiotics fermentation plant, in Rochester, New York.

DuPont's is marketing its 2'FL HMO, branded as CARE4U, to consumer manufacturers who can use it in adult supplements for digestive and immune health, said Ratna Mukherjea, global research and development leader at DuPont.

DuPont is researching how to produce more of the 130 or so HMO varieties found in breast milk as the company identifies those with the most potential health benefits, Mukherjea said. More HMO varieties are already in the commercial pipeline.

"This is just the beginning for HMO,'' she said.