Research news in brief

Salty diets may raise blood pressure by killing off gut bacteria

According to German research published by Nature, high salt intake alters the gut microbiota in mice. As the role of gut microbiota in disease is becoming increasingly recognised, these findings highlight the gut microbiome as a potential therapeutic target to counteract salt-sensitive conditions. High salt consumption associated with a Western lifestyle can lead to hypertension and cardiovascular disease. It may also drive autoimmunity by inducing pro-inflammatory T-helper-17 (TH17) cells, which have also been linked to hypertension. To determine the effect of high salt consumption on the composition of the gut microbiota, the researchers analysed faecal samples from mice fed a normal salt diet and a high salt diet (HSD). The authors found that by day 14, several microbial species were significantly decreased in HSD-fed mice. They then used 16S ribosomal DNA gene sequencing and computational approaches to identify the most important bacterial groups that decreased when mice were fed a HSD and found that depletion of a member of the genus Lactobacillus (Lactobacillus murinus) was most strongly associated with HSD. Further work showed that administration of L. murinus to mice reduced TH17 cells and prevented salt-induced aggravation of actively induced experimental autoimmune encephalomyelitis (a mouse model of brain inflammation) and salt-sensitive hypertension. In line with these findings, a small pilot study in healthy humans found that increased salt intake reduces intestinal survival of multiple Lactobacillus species, accompanied by an increase in TH17 cells and elevated blood pressure; although further investigation in humans is required.

Heavy smoking and drinking makes us look older

Heavy drinking and smoking are linked to visible signs of physical ageing and looking older than one’s years, according to Danish research published by the Journal of Epidemiology and Community Health. Light to moderate drinking was not associated with biological ageing, the findings showed. But nor was it linked to the slowing of the visible ageing process, as there was no difference in the prevalence of the signs of ageing between light to moderate drinkers and non-drinkers, the researchers point out. They base their findings on information from more than 11 500 adults, whose heart health and visible ageing signs were tracked for an average of 11.5 years as part of the Copenhagen City Heart Study. This study, which began in 1976, has been monitoring a random sample of Danish people over the age of 20 years living in the Copenhagen area in 1981–1983, 1991–1994 and 2001–2003. Before each of the clinic visits, participants were quizzed about their lifestyle and general health and asked to state how much they drank and smoked. They were also checked for four signs of ageing that have previously been linked to a heightened risk of cardiovascular ill health or death – earlobe creases, a greyish opaque coloured ring or arc around the peripheral cornea of both eyes (arcus corneae), yellow-orange plaques on the eyelids (xanthelasmata), and male pattern baldness (receding hairline or a bald patch on the top of the head). The average age of the participants was 51 years, but ranged from 21 to 86 years among the women, and from 21 to 93 years among the men. Average alcohol consumption was 2.6 drinks per week for women and 11.4 for men. Just over half the women (57%) and around two-thirds of the men (67%) were current smokers. Arcus coneae was the most common sign of ageing among both sexes, with a prevalence of 60% among men aged over 70 years and among women aged over 80 years. The least common sign was xanthelasmata, with a prevalence of 5% among men and women aged over 50 years. A receding hairline was common among men, with 80% of those over the age of 40 years being affected. Analysis of drinking and smoking patterns revealed a consistently heightened risk of looking older than one’s true age and developing arcus corneae, earlobe creases and xanthelasmata among people who smoked and drank heavily.

Our brain processes what we hear in waves

Australian and Italian researchers have provided important new evidence for the cyclical nature of perception in an article published in Current Biology. They showed that sensitivity for detecting weak sounds is not constant, but fluctuates rhythmically over time. The oscillation in sensitivity occurs between the two ears, first one then the other, swapping every 10th of a second. The oscillation is so fast that we are normally unaware of it, but can be revealed using highly sensitive experiments. Oscillations have been previously reported in the visual system but not in audition, suggesting that vision is special. One reason for the failure to find auditory oscillations is that previous researchers measured sensitivity for the two ears together, whereas the new work shows that sensitivity alternates between the two ears, a subtle fact missed by previous measurements. The new findings are important for many reasons. First, they show that oscillations are a general feature of perception, not specific to vision. Second, there was clear evidence for alternation of sensitivity between the two ears, suggesting that the brain samples from the two ears alternately, focusing attention on one ear at a time, probably a clever trick used by the brain to tag the ear of origin which is important for many perceptual tasks. Third, the study showed that not only does sensory sensitivity alternate at a specific rhythm, but decision making also oscillates at a subtly different frequency.

Is vitamin D linked to fertility treatment success?

UK researchers are calling for a randomised clinical trial to be carried out to investigate the potential role of vitamin D supplementation in improving live birth rates after an assisted reproduction treatment (ART). This follows a review and meta-analysis published in Human Reproduction that shows a strong link between low vitamin D concentrations (£ 75 nmol/L) in women and lower live birth rates after ART compared with women who have adequate levels of vitamin D (> 75 nmol/L) in their bodies. The researchers cautioned that their findings did not mean that vitamin D supplementation necessarily improved women’s chances of having a baby after ART, as their research can only show an association and not that having sufficient concentrations of vitamin D actually cause the improved birth rate. The researchers analysed data from 11 published studies that included 2700 women who were undergoing ART (in vitro fertilisation, intracytoplasmic sperm injection or frozen embryo transfer) and whose vitamin D status had been checked through blood tests. They found that live births were a third more likely to occur in women who were replete with vitamin D when compared with women who were not. Vitamin D concentrations of more than 75 nanomoles per litre of blood (nmol/L) were considered sufficient, concentrations of less than 75 nmol/L were considered insufficient, and less than 50 nmol/L were considered deficient. A similar result was seen when the researchers looked at the results of pregnancy tests and clinical pregnancies (where a fetal heartbeat could be detected). When compared with women who had deficient or insufficient concentrations of vitamin D, women who had sufficient vitamin D were 34% more likely to have a positive pregnancy test and 46% more likely to achieve a clinical pregnancy. No associations were found between miscarriage and vitamin D concentrations.

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