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Air pollution is linked to so many negative health effects, now another one - poorer quality sperm. In this study 6475 males  (ages ranged from 15–49 years) had their sperm analyzed as part of a standard medical examination program in Taiwan. They were also able to get air pollution measurements for each person's address for that time period. They found that both short-term and long-term exposure to higher levels of fine particulate matter (PM2.5) pollution were linked to lower numbers of sperm being normal in size and shape (sperm morphology), but with a higher concentration of sperm. Perhaps a  compensatory phenomenon?

The researchers pointed out that other studies have also found effects from air pollution on sperm. Since this study only analyzed a person's sperm one time, the findings are correlational (they observed an association, but couldn't definitely say it caused the effect). [Some other posts on sperm qualityhere, here, here.] From Medical Xpress:

Air pollution linked to poorer quality sperm

Air pollution, particularly levels of fine particulate matter (PM2.5), is associated with poorer quality sperm, suggests research published online in Occupational & Environmental Medicine. Although the size of the effect is relatively small in clinical terms, given how widespread air pollution is, this might spell infertility for a "significant number of couples," say the researchers.

Environmental exposure to chemicals is thought to be a potential factor in worsening sperm quality, but the jury is still out on whether air pollution might also have a role. To explore this possibility further, the international team of researchers looked at the impact on health of short and long term exposure to fine particulate matter (PM2.5) among nearly 6500 15 to 49 year old men in Taiwan.

The men were all taking part in a standard medical examination programme between 2001 and 2014, during which their sperm quality was assessed (total numbers, shape/size, movement) as set out by World Health Organization guidelines. PM2.5 levels were estimated for each man's home address for a period of three months, as that is how long it takes for sperm to be generated, and for an average of 2 years, using a new mathematical approach combined with NASA satellite data.

A strong association between PM2.5 exposure and abnormal sperm shape was found. Every 5 ug/m3 increase in fine particulate matter across the 2 year average was associated with a significant drop in normal sperm shape/size of 1.29 per cent. And it was associated with a 26 per cent heightened risk of being in the bottom 10 per cent of normal sperm size and shape, after taking account of potentially influential factors, such as smoking and drinking, age or overweight. However, it was also associated with a significant increase in sperm numbers, possibly as a compensatory mechanism to combat the detrimental effects on shape and size, suggest the researchers. Similar findings were evident after three months of exposure to PM2.5. [Original study.]

There are a number of professions where there is an elevated risk for getting chronic obstructive pulmonary disease (COPD) from all the vapors, gases, dust, fumes, and chemicals (all irritants) that one inhales - such as welders, coal miners, cotton textile workers, construction, farmers, even hairdressers. Now a study suggests that nurses who use disinfectants at least once a week are also at higher risk for COPD. The specific disinfectants associated with COPD are glutaraldehyde, bleach, hydrogen peroxide, alcohol, and quats (quaternary ammonium compounds).

From Medscape: Exposure to Disinfectants Linked to COPD

The risk for chronic obstructive pulmonary disease (COPD) is higher in those who use disinfectants at least once a week than in those who do not, a preliminary observational study of a large cohort of female nurses in the United States reveals. 

For their study, Dr Dumas and her colleagues analyzed data from the Nurses' Health Study II. From 2009 to 2017, participants completed a survey every 2 years. ..... And they used the job-task exposure matrix to evaluate seven major disinfectants: formaldehyde, glutaraldehyde, hypochlorite bleach, hydrogen peroxide, alcohol, quaternary ammonium compounds (or quats), and enzymatic cleaners.

In the cohort of 55,185 women who were nursing in 2009, 663 reported incident physician-diagnosed COPD during the follow-up period. The team found an association between incident COPD and high-level exposure to glutaraldehyde, bleach, hydrogen peroxide, alcohol, and quats. Of the nurses diagnosed with COPD, 37% reported the weekly use of disinfectants to clean surfaces, and 19% reported weekly use to clean instruments. Regression models demonstrated that the risk for COPD was 22% higher for nurses who cleaned instruments, and 32% higher for nurses who cleaned surfaces.

We've been aware of the association between disinfectants and asthma for some time, she told Medscape Medical News.... There's no easy solution, Dr Dumas acknowledged. "Protection from infection is important, but so is the health of workers." Green products might be one solution, "but we're not sure of their effect on health either. Just because they're natural, doesn't mean they're safe; they can have allergens." Another solution could be ultraviolet light, as previously reported by Medscape Medical News.

This was a "well-performed study," said Lidwien Smit, PhD, from the University of Utrecht in the Netherlands. "I just wonder about the pathology, and how it influences the microbiome. Disinfectants are meant to kill off bacteria, but if you're exposed to large concentrations, you're also inhaling them, which could affect your airway microbes," she explained. In fact, disinfectants could play a role in killing off bacterial communities in the airways that are responsible for "immune homeostasis" and keep users healthy, she added. If that immune balance gets disturbed, it might have an influence on a person's reaction to pathogens or inflammation. 
Chest X-ray of person with COPD. Credit: Wikipedia

An interesting possibility - that taking supplements of  a type of vitamin E known as gamma tocopherol may reduce the inflammation of the airways common in asthma patients – eosinophilic inflammation.

Note that these findings were from a preliminary study of 15 people with mild asthma, done by researchers at the Univ. of North Carolina. Now larger and longer studies need to be done, especially to make sure that side-effects and an increased risk for hemorrhagic stroke won't occur with gamma tocopherol, as it does for the other form of vitamin E (alpha tocopherol) commonly found in supplements. From Medical Xpress:

Can asthma be controlled with a vitamin supplement?

The shortness of breath experienced by the nearly 26 million Americans who suffer from asthma is usually the result of inflammation of the airways. People with asthma typically use albuterol for acute attacks and inhaled steroids to limit chronic inflammation. Both medications come with side effects. But what if it was possible to keep asthma under control by changing one's diet or taking a vitamin supplement? It may happen sooner than you think.

Preliminary research results from the UNC School of Medicine indicate that a type of vitamin E known as gamma tocopherol may reduce eosinophilic inflammation – a kind of airway inflammation common in asthma patients. The results were published in the Journal of Allergy & Clinical Immunology.

"We started looking into vitamin E because epidemiologic data suggested that people with high amounts of vitamin E in their diet were less prone to asthma and allergic disease," said Michelle Hernandez, MD, professor of pediatrics and senior author of the study.  There are several different isoforms of vitamin E. The type commonly found in vitamin supplements – alpha tocopherol – has been studied previously, but the results suggested that alpha tocopherol was not particularly effective. Even worse, the alpha isoform seemed to be associated with an increased risk for hemorrhagic stroke.

So UNC researchers took a different tack and asked whether the kind of vitamin E being used might have an effect on the outcome. They began looking more closely at gamma tocopherol, the type of vitamin E commonly found in a diet rich in nuts and nut oil. .... "While the alpha isoform does have antioxidant activities, gamma tocopherol has both an antioxidant and a very unique anti-inflammatory action as well," she said "That anti-inflammatory effect is what we think made the difference in this study."

Participants in the study were randomized into two groups that received either gamma tocopherol supplement or a placebo for two weeks. At the end of that period, they were asked to cough up sputum..... After a three week "washout period" where they took nothing, subjects were placed in the other group: if they took the supplement for the first two weeks, they took a placebo for the second period.

"The advantage of a cross-over design like this is that we are able to compare the subjects to themselves," said Burbank. "And what we found is that when people were taking the vitamin E supplement, they had less eosinophilic inflammation." In addition to decreased inflammation, those who were taking vitamin E were also found to have lower levels of proteins called mucins, which affect the stickiness of mucus. Mucins are often elevated in asthmatics.

A large study by researchers at the State University of NY, of 65,869 postmenopausal women found that those who have a history  of gum or periodontal disease also have an overall higher risk of cancer. The women with a history of periodontal disease also had an increased risk for several specific cancers: breast, esophageal, gallbladder, lung and melanoma cancers. This cancer and gum disease association occurred in both nonsmokers and smokers.

How is periodontal disease "promoting" cancer? How it occurs is still unclear, but one theory suggests the gum disease bacteria are in the saliva, which is swallowed, and so the bacteria get into the gut, esophagus, or lungs. Or bacteria from diseased gum tissues get into "systemic circulation" and so get to distant sites in the body.  One of the researchers pointed out that "Certain periodontal bacteria have been shown to promote inflammation even in tiny amounts, and these bacteria have been isolated from many organ systems and some cancers including esophageal cancers."

From Medscape: Gum Disease and Increased Link to Many Cancers

Brushing, flossing, and regular dental checkups appear to do much more than maintain a healthy smile. Now, a large prospective cohort study shows that postmenopausal women with a history of periodontal disease, including those who have never smoked, are at significantly increased overall risk for cancer as well as site-specific cancers, including lung, breast, esophageal, gallbladder, and melanoma skin cancers.

The study authors note that these results add to the growing body of evidence from smaller studies and studies in men that link periodontal disease to total cancer risk. The Centers for Disease Control and Prevention (CDC) estimate that 47% of adults 30 years of age and older in the United States have some form of periodontal disease, ranging from mild to severe. At age 65 years and older, however, 70% of adults have moderate to severe periodontal disease, according to the CDC.

The study involved almost 66,000 postmenopausal women in the United States, who were enrolled in the ongoing Women's Health Initiative Observational Study (WHI-OS). During a mean follow-up of 8.32 years, the team identified 7149 cancers and found that periodontal disease history was associated with a 14% increased total cancer risk. When analyses were limited to 34,097 never-smokers, there was also an increased risk for overall cancer.

An association between periodontal disease and site-specific cancers was observed in breast, lung, esophageal, gallbladder, and melanoma skin cancers. There was a borderline association with stomach cancer, the study authors report, and periodontal disease was not associated with cancers of the pancreas; liver; lower digestive tract organs; or lip, oral cavity, and pharynx combined. Similarly, there was no association with genitourinary and lymphoid and hematopoietic malignancies.

For the study, the investigators looked at periodontal disease information in 65,869 women aged 54 to 86 years at 40 US centers. Mean age was 68 years. Most women were non-Hispanic whites with some college education. All participants answered the question "Has a dentist or dental hygienist ever told you that you had periodontal or gum disease? (No/Yes)" between 1999 and 2003 on the annual Year-5 WHI-OS follow-up questionnaire. Cancer outcomes were documented through September 2013 with a maximum 15-year follow-up period.

 Women who reported a history of periodontal disease were also more likely to report a history of smoking, secondhand smoke exposure, alcohol use, hormone therapy (estrogen plus progestin), and a cancer diagnosis, the study authors report. At the same time, no significant differences were observed in body mass index, physical activity levels, or history of diabetes between women with periodontal disease and those without. [Original study.]

It's reassuring to see that there are positive things one can do to maintain brain health as one ages. With normal aging, the brain typically shrinks a little with each passing decade  - starting from about the age of 40. But one recent Australian study, which reviewed the results of many other studies, found that exercise slows down this shrinkage in humans, specifically in the left hippocampus. That is, that aerobic exercise had a significant positive effect on the volume of the left hippocampus. This matches the result of animal studies.

The researchers pointed out that some studies found increases also in other parts of the human brain from exercise (e.g. in the white matter), but that they did not look at and review those studies. [See posts on research.] The good news is that positive effects were from exercise programs generally lasting less than 12 months. But it is unknown which type of exercise is best, or whether it is general "activity level and movement" that is most important. Bottom line: Get out there and move, move, move for brain health. And for cardiorespiratory fitness. It's all linked and it's all good. From Medical Xpress:

Exercise maintains brain size, new research finds

Aerobic exercise can improve memory function and maintain brain health as we age, a new Australian-led study has found. In a first of its kind international collaboration, researchers from Australia's National Institute of Complementary Medicine at Western Sydney University and the Division of Psychology and Mental Health at the University of Manchester in the UK examined the effects of aerobic exercise on a region of the brain called the hippocampus, which is critical for memory and other brain functions.

Brain health decreases with age, with the average brain shrinking by approximately five per cent per decade after the age of 40. Studies in mice and rats have consistently shown that physical exercise increases the size of the hippocampus but until now evidence in humans has been inconsistent.

The researchers systematically reviewed 14 clinical trials which examined the brain scans of 737 people before and after aerobic exercise programs or in control conditions. The participants included a mix of healthy adults, people with mild cognitive impairment such as Alzheimer's and people with a clinical diagnosis of mental illness including depression and schizophrenia. Ages ranged from 24 to 76 years with an average age of 66. The researchers examined effects of aerobic exercise, including stationary cycling, walking, and treadmill running. The length of the interventions ranged from three to 24 months with a range of 2-5 sessions per week.

Overall, the results – published in the journal NeuroImage– showed that, while exercise had no effect on total hippocampal volume, it did significantly increase the size of the left region of the hippocampus in humans.

"When you exercise you produce a chemical called brain-derived neurotrophic factor (BDNF), which may help to prevent age-related decline by reducing the deterioration of the brain," Mr Firth said. "Our data showed that, rather than actually increasing the size of the hippocampus per se, the main 'brain benefits' are due to aerobic exercise slowing down the deterioration in brain size. In other words, exercise can be seen as a maintenance program for the brain.".... Interestingly, physical exercise is one of the very few 'proven' methods for maintaining brain size and functioning into older age.

A recent study looked at 2 specific antioxidant levels in a variety of mushroom species. Mushrooms are an excellent source of nutrients, such as riboflavin and other B vitamins, selenium, copper, potassium, dietary fiber, as well as high levels of antioxidants ergothioneine (ERGO) and glutathione (GSH). The study found the highest levels of these antioxidants in yellow oyster and porcini mushrooms.

Ergothioneine (ERGO), which is found throughout the human body, is a critical antioxidant that acts with other antioxidants to protect against oxidative stress in the mitochondria (in our cells). What foods are good sources of ERGO? Mushrooms have the highest levels, but other foods with high ERGO content include red beans, black beans, kidney beans, oat bran, liver, and king crab.

Glutathione (GSH) is produced by the body and found in every cell - thus the major antioxidant within cells. It also helps the liver remove chemicals (detoxification) of a wide range of toxins, drugs, pollutants, and carcinogens, and maintenance of immune functioning. Low GSH levels are associated with increased risks for cancer, cardiovascular diseases, arthritis and diabetes. So you want to maintain optimal tissue levels of GSH (through dietary intake) because it is so critical for maintaining health. What foods are good sources of GSH? Mushrooms, and many fresh (raw) fruits and vegetables, including asparagus, avocados, potatoes, spinach, squash, tomatoes. Also fresh, uncooked meats and dairy products (raw milk) and eggs. From Science Daily:

Mushrooms are full of antioxidants that may have antiaging potential

Mushrooms may contain unusually high amounts of two antioxidants that some scientists suggest could help fight aging and bolster health, according to a team of Penn State researchers. In a study, researchers found that mushrooms have high amounts of the ergothioneine and glutathione, both important antioxidants, said Robert Beelman, professor emeritus of food science and director of the Penn State Center for Plant and Mushroom Products for Health. He added that the researchers also found that the amounts the two compounds varied greatly between mushroom species.

Beelman said that when the body uses food to produce energy, it also causes oxidative stress because some free radicals are produced. Free radicals are oxygen atoms with unpaired electrons that cause damage to cells, proteins and even DNA as these highly reactive atoms travel through the body seeking to pair up with other electrons. Replenishing antioxidants in the body, then, may help protect against this oxidative stress.

According to the researchers, who report their findings in a recent issue of Food Chemistry, the amounts of ergothioneine and glutathione in mushrooms vary by species with the porcini species, a wild variety, containing the highest amount of the two compounds among the 13 species tested. The more common mushroom types, like the white button, had less of the antioxidants, but had higher amounts than most other foods, Beelman said....Mushrooms that are high in glutathione are also high in ergothioneine, for example. Cooking mushrooms does not seem to significantly affect the compounds, Beelman said.

"It's preliminary, but you can see that countries that have more ergothioneine in their diets, countries like France and Italy, also have lower incidents of neurodegenerative diseases, while people in countries like the United States, which has low amounts of ergothioneine in the diet, have a higher probability of diseases like Parkinson's Disease and Alzheimer's," said Beelman. "Now, whether that's just a correlation or causative, we don't know." [Original study.]

The following study was done in England, but the results should be taken seriously and may (probably) apply to the US also - painted and enameled glassware ("externally decorated glassware") may contain high levels of lead and cadmium. The researchers found that more than 70% of the products (52 out of 72) tested positive for lead, and the metal was found in all colors, including the decorated gold leaf of some items. A similar number (51 out of 72) tested positive for cadmium, with the highest concentrations usually encountered in red enamel.

They found this in products manufactured both in Europe and China - which is why I think the results apply to painted or decorated glassware in the USA also. It probably also applies to some (many?) painted ceramics. So beware!  If you use painted or enameled glassware, you are at increased risk for ingesting lead and cadmium, both of which are linked to health problems - especially for developing fetuses and children. The best safe level of each is zero. The researchers mention that there are newer alternatives that are safe (lead and cadmium free). From Science Daily:

Drinking glasses can contain potentially harmful levels of lead and cadmium

Enameled drinking glasses and popular merchandise can contain potentially toxic levels of lead and cadmium, a study has shown. Researchers at the University of Plymouth carried out 197 tests on 72 new and second-hand drinking glass products, including tumblers, beer and wine glasses, and jars.

They found lead present in 139 cases and cadmium in 134, both on the surface of the glasses and, in some cases, on the rims, with concentrations of lead sometimes more than 1000 times higher than the limit level. Tests showed that flakes of paint often came away from the glass under when simulating sustained use, indicating the substances could be ingested over a prolonged period.

The study, published in Science of the Total Environment, analysed a range of glassware using portable x-ray fluorescence (XRF) spectrometryMore than 70% of the products (52 out of 72) tested positive for lead, and the metal was found in all recorded colours, including the decorated gold leaf of some items. A similar number (51 out of 72) tested positive for cadmium, with the highest concentrations usually encountered in red enamel.

The lead concentrations ranged from about 40 to 400,000 parts per million (ppm), while quantities of cadmium ranged from about 300 to 70,000 ppm. According to the US Office of Environmental Health Hazard Assessment, the limit levels for the externally decorated lip area of drinking glass are 200 ppm and 800 ppm respectively.

In the research, Dr Turner highlights that the Federation of European Screen Printers Associations says organic inks are becoming more popular than metallic pigments because of environmental concerns, and that such inks were evident on a number of newly-purchased products which proved negative for lead and cadmium.

He also says that additional analyses confirmed that hazardous elements are also used to decorate a wider range of consumer glassware that has the potential to be in contact with food, including the exteriors of bottles for the storage of beer, wine or spirits, the external text and logos on egg cups, jugs and measuring cups, and the undersides of coasters and chopping boards. "Given that safer alternatives are available to the industry, the overall results of this study are both surprising and concerning," Dr Turner added. "Why are harmful or restricted elements still being employed so commonly to decorate contemporary glassware manufactured in China, the European Union and elsewhere? " [Original study.]

A recent study found that significantly increasing  dietary fiber intake after a diagnosis of colorectal cancer was associated with a lower death rate - from both colorectal cancer and overall mortality (from any cause). The 1575 men and women (all healthcare professionals) in the study had received a nonmetastatic colorectal cancer diagnosis (it had not spread beyond the colon), and the follow-up was about 8 years. These results were from food, not supplements.

How much did extra dietary fiber lower the death rate? For each additional 5  grams of fiber added to their daily diet (after diagnosis) was associated with a 18% lower colorectal cancer death rate, and a 14% lower death rate from any cause. In this study, whole grains, especially in cereals, were found to be the most beneficial. Current dietary guidelines recommend a fiber intake of 25 to 38 grams per day, but most Americans eat far lessDietary fiber is found in plant foods, such as beans, whole grains, nuts, seeds,  vegetables, and fruits. Plant fiber feeds the millions of gut microbes, especially beneficial microbes (here, here, and here) - something that was not really discussed in the study.

The researchers pointed out that a high fiber diet (especially from whole grains and cereals) is linked to a lower risk of getting colorectal (colon) cancer in the first place.  Also, that "higher intake of fiber, especially cereal fiber", has been linked to improved insulin sensitivity, reduced inflammation, type 2 diabetes, cardiovascular disease, and total mortality. Other studies have found that  vitamin D supplementation, exercise, and eating fish all increase survival from colorectal cancer. From From Medical Xpress:

Fiber-rich diet boosts survival from colon cancer

A diet rich in fiber may lessen the chances of dying from colon cancer, a new study suggests. Among people treated for non-metastatic colon cancer, every 5 grams of fiber added to their diet reduced their odds of dying by nearly 25 percent, said lead researcher Dr. Andrew Chan. He is an associate professor in the department of medicine at Harvard Medical School.

"What you eat after you've been diagnosed may make a difference," Chan said. "There is a possibility that increasing your intake of fiber may actually lower the rate of dying from colon cancer and maybe even other causes." Chan cautioned, however, that the study does not prove that the additional fiber caused people to live longer, only that the two were associated.

Fiber has been linked to better insulin control and less inflammation, which may account for better survival, he suggested. In addition, a high-fiber diet may protect people from developing colon cancer in the first place. The greatest benefit was attributed to fiber from cereals and whole grains, according to the report. Vegetable fiber was linked to an overall reduction in death, but not specifically in death from colon cancer, and fiber from fruit was not linked to a reduction in death from any cause. 

For the study, Chan and his colleagues collected data on 1,575 men and women who took part in the Nurses' Health Study and Health Professionals Follow-up Study, and who had been treated for colon or rectal cancer that had not spread beyond the colon. Specifically, the study looked at total fiber consumption in the six months to four years after the participants' cancer diagnosis. The researchers also looked at deaths from colon cancer and any other cause. In an eight-year period, 773 participants died, including 174 from colorectal cancer. [Original study.]

Another study has shown health benefits from eating a diet rich in whole grains, as compared to one with lots of refined grains (think bagels, muffins, white bread). Fifty overweight Danish adults were randomly assigned to either a group where all grains eaten were whole grains or a group where all grain products were of refined grains. They did this for 8 weeks, then ate their usual diet for a few weeks (the "washout period"), and then were assigned to the other dietary group for 8 weeks.

They found that eating the diet rich in whole grains resulted in: consuming fewer calories (the whole grains made them feel fuller), losing weight, and a decrease in chronic low-grade inflammation (by measuring blood inflammation markers). The whole grain rye seemed to be especially beneficial. But interestingly, the researchers found that the whole grain diet did not significantly change the gut microbe composition. But they did find that 4 strains of Faecalibacterium prausntzii and one of Prevotella copri increased in abundance after whole grain and decreased after refined grain consumption. F.prausnitzii is a desirable and beneficial keystone species in the gut (here and here).

Other studies show that eating a diet rich in whole grains (rather than refined grains) is associated with a decreased risk of several diseases, including type 2 diabetes and cardiovascular diseases. Bottom line: choose whole grains whenever possible. From Science Daily:

Several reasons why whole grains are healthy

When overweight adults exchange refined grain products -- such as white bread and pasta -- with whole grain varieties, they eat less, they lose weight and the amount of inflammation in their bodies decreases. These are some of the findings of a large Danish study headed by the National Food Institute, Technical University of Denmark. 

The study included 50 adults at risk of developing cardiovascular disease or type 2 diabetes. Blood tests showed that the participants had less inflammation in their bodies when eating whole grains. In particular, it appeared that rye had a beneficial effect on the blood's content of inflammatory markers. Inflammation is the natural response of the body to an infection, but some people have slightly elevated levels of inflammation (so-called low-grade inflammation) even though there is no infection. This is particularly the case in overweight people. In overweight people, an increased level of 'unnecessary' (subclinical) inflammation may lead to increased risk of developing type 2 diabetes.

The study also shows that participants eat less when whole grain products are on the menu -- presumably because whole grain consumption causes satiety. While eating the whole grain diet, participants have generally lost weight. The researchers used DNA sequencing to analyze stool samples from the participants in order to examine whether the different diet types affected the participants' gut bacteria composition. Overall, the analysis did not shown major effects of the dietary grain products on the composition of the gut bacteria. [Original study.]

A while ago I posted the results of studies showing differences in infant  microbiomes (community of microbes) depending on whether the babies were delivered vaginally or by C-section, and also that "vaginal seeding" may eliminate some of these differences. [C-section babies also have a higher incidence of some health issues, such as allergies, asthma, etc.] Well....that research generated a lot of controversy both for and against, and resulted in many women requesting that "vaginal seeding" be done to their babies after they were delivered by C-section. Even the noted microbiome researcher Rob Knight publicly admitted that the procedure was done to his baby after his partner received a C-section.

Vaginal seeding is the process of swabbing the bodies of C-section babies (including the mouth and nose) with a gauze pad containing the vaginal fluids from their mothers in the minutes after birth - so that the baby is exposed to the same maternal microbes as a baby born vaginally (because mothers transmit microbes to the baby as it moves through the birth canal). Initial research showed this made the microbiomes of the C-section babies look a lot like vaginally born babies, especially their skin and oral microbiomes, but whether these differences persist after a few months is unclear.

Now the American College of Obstetrics and Gynecology (ACOG) has come out with a position paper that vaginal seeding should not be done to babies, except as part of an official clinical trial. Their main opposition to the procedure is fear of transmitting pathogenic bacteria or viruses (e.g. group B streptococci, and STDs). The main reasons in support of doing the  vaginal seeding procedure is the body of research finding differences among C-section and vaginally delivered babies (allergies, asthma, etc.), and the concern that at least some of this may be due to lack of  exposure to maternal vaginal microbes during delivery. Instead, ACOG suggests breastfeeding the baby to transmit maternal microbes to the baby to "seed the gut". And if "a patient insists on performing the procedure herself, ACOG recommends ob-gyns have a documented discussion of the potential risks".

As can be expected, there is an outcry and rejection by some (many?) of the ACOG position paper. At least the ACOG paper acknowledges that every woman can make her own decision regarding this issue, even though they may not support it. And absolutely everyone agrees that more research is needed. From Ars Technica:

Doctors warn new parents: Step away from the vaginal fluid swabs

To slather, or not to slather—that is the question that has been roiling doctors, scientists, and new parents recently. And a new ruling by a doctor’s group stands to muck up the debate further. Amid the birth of microbiome research, some scientists have advocated for smearing bacteria-laden vaginal secretions on any newborns who missed out—namely those born via Caesarian section. Scientists keenly hypothesize that such a gooey glaze can “seed” a more-or-less sterile infant with life-long microbial companions. These wee chums may help train an infant's immune system and dodge issues like allergies and asthma later in life. Several studies have indeed found correlations between C-section deliveries and higher risks of those conditions.

In the latest turn to the controversy, the American College of Obstetricians and Gynecologists’ (ACOG) Committee on Obstetric Practice issued a November opinion firmly wiping up the slimy idea. In its opinion, the committee said it: “…does not recommend or encourage vaginal seeding outside of the context of an institutional review board-approved research protocol, and it is recommended that vaginal seeding otherwise not be performed until adequate data regarding the safety and benefit of the process become available.”

The few studies we do have on infant microbiomes provide no clear answers on the significance of an early “seeding” for health. A 2016 review looking at the patterns of microbial communities in the guts of infants in their first year found that C-section babies did show differences in the first three months. However, those differences disappeared by six months. Similarly, a small study of 18 babies also published last year found that vaginal seeding could eliminate microbial differences between vaginally and C-section delivered babies. But the study only looked at the infants' microbiomes in that first month, and the health effects—if any—are unknown.

The most concerning thing about vaginal seeding, the committee argues, is the potential for transmitting pathogens, such as herpes simplex virus, human papilloma virus (HPV), group B streptococci, and Neisseria gonorrhea. .... If a woman insists on the seeding, the committee recommended she be thoroughly tested and informed of the risks—as well as discouraged.