- In a new study, individuals rated as attractive had higher rates of phagocytosis of E. coli bioparticles, higher basophil white blood cell counts, and lower neutrophil white blood cell counts.
- Female participants rated photos of males with high functioning natural killer (NK) cells as being more attractive. NK cells are immune cells that defend against viral infections and cancer.
- Male participants rated photos of females with low functioning NK cells as more attractive.
- Male participants rated photos of females with slower rates of S. aureus growth in their plasma as more attractive than females with faster rates of S. aureus growth. This effect was absent in males.
Scientists who study the evolution of humans have long postulated that the individuals considered the most “good-looking” may also be healthier.
“[I]t’s been long theorized that this relationship should exist,” Summer Mengelkoch, a doctoral candidate in experimental social psychology at Texas Christian University and lead author of a new study on the topic, told Medical News Today, “but no one’s really studied it very directly before.”
A number of scholars, the researchers of the new study write, have found features such as symmetrical and average faces to be considered attractive across cultural groups. In the past, researchers have suggested these preferences may be linked to those who possess these traits being better reproductive partners because they’re healthy with strong immune function.
For the new study published in Proceedings of the Royal Society B: Biological Sciences, the researchers set out to “address this empirical gap” by examining links between physical appearance and immune function.
Study used stringent criteria for selecting participants
The researchers recruited 159 people who were students at Texas Christian University or members of the nearby community. Participants ranged from 17–30 years old. About 67% were white, about 15% Hispanic, about 6% Asian or Pacific Islanders, and less than 5% Black.
Participants needed to be free of chronic medical conditions to take part, including mental illness, have a body mass index (BMI) of less than 30, have not suffered from acute illness for 2 weeks leading up to the study, not be taking hormonal contraceptives, be willing to abstain from steroids and anti-inflammatory medicines, exercise and alcohol for 2 days prior to the study, and be willing to fast the morning of the study.
Females participated in the study during the early follicular phase of their ovulatory cycle to control for the impact of sex steroid hormones on immune function and inflammatory processes.
All participants completed demographic and lifestyle questionnaires. They were then photographed from the neck up while wearing neutral facial expressions and after removing any cosmetics. Researchers then measured their height and weight and drew a blood sample.
Researchers tested the participants’ blood for several factors, including how their peripheral blood mononuclear cells (PBMCs) responded to various immunological stimulants, the functional level of their NK cells, and S. aureus growth in plasma to identify the participants’ antibacterial defenses.
The work gave Mengelkoch an idea of why researchers looking at the connection between physical attractiveness and health in the past examined more limited, often secondary, biological markers of immunological function. “Doing immune function research was hard, and so I get why people haven’t done it before,” she told MNT.
Next, researchers collected facial attractiveness ratings from 492 participants between 18–29 years. Of the participants, 259 were females, and 233 were males. About 60% of participants were white, about 20% Black, about 12% Hispanic, and about 9% Asian.
Participants rated randomly selected 25 photos of members of the opposite sex on characteristics, which included factors such as attractiveness and health.
Sex-specific features of attractiveness
Participants identified as attractive had higher rates of phagocytosis of E. coli bioparticles. Phagocytosis is the process by which certain types of white blood cells destroy microbes and damaged host cells. Those with higher levels of phagocytosis are thought to be less likely to experience microbial infections. This implies, Mengelkoch told MNT, “that we might find people who can efficiently deal with bacterial threats to be really attractive.”
Female participants found photographs of males who have high functioning NK cells as being more attractive than those with low functioning NK cells. In the study, the researchers explain, this suggests females may prefer males who are well-suited to combat viral threats and neoplastic growth.
On the other hand, male participants rated photographs of females who had low functioning NK cells as more attractive. The researchers point out that some scholars have noted NK cell function is lower with the presence of high estrogen. A 2005 study found that women who were not wearing makeup with higher levels of late follicular estrogen had faces considered more attractive and feminine.
“So I think what’s going on there,” Mengelkoch told MNT, “is that there’s kind of this confounding effect where estrogen is ‘good’ for women’s attractiveness, but not so good for this specific measure of immune function.”
Additionally, the study found that women with slower rates of S. aureus growth in their plasma were perceived as more attractive than women with faster rates of S. aureus growth in their plasma. A similar effect was not observed with men.
Researchers found no significant relationships between attractiveness and cellular proliferation or cytokine production. Higher levels of cytokine release indicate a more robust immune function.
Logan Pearce, a social psychology graduate student at Princeton, wondered why the study’s authors kept certain individuals from participating in the study. “They excluded people who have a mental illness [and] obese people,” Pearce told MNT. “I wasn’t quite sure why they did that.”
In a follow-up email, Mengelkoch explained that “obese people, people with chronic illnesses and people with mental illnesses all have higher levels of inflammation than do non-obese, illness-free people,” she wrote. “[T]hese are standard inclusion criteria for a study looking at differences in immune response.”
Pearce also wondered why the study was designed to have participants rate the attractiveness of participants of the opposite sex. “This study is kind of assuming everyone is straight,” Pearce told MNT.
The study’s authors did collect data on the participants’ sexuality. About 83% of the participants rating the photographs said they were heterosexual, about 11% said they were bisexual, and about 5% said they were homosexual.
Mengelkoch wrote in an email that the researchers ran a series of analyses and found no significant differences in how heterosexual and nonheterosexual participants rated the photos.
“That is, people of all sexual orientations rated people the same on attractiveness (and the other characteristics),” she wrote. “We had a small-ish sample of nonheterosexual raters, so no conclusions can really be drawn from that, but there was no cause to toss their data.”
In the study, the researchers write that future studies are needed to look at the relationships between facial attractiveness, NK cell cytotoxicity, facial femininity, and female’s estrogen levels.
Mengelkoch would also like to see a study that looks at participants who have an illness.
For this study, researchers took photographs of participants who were basically healthy. Doing that made it easier, Mengelkoch explained, to “compare some of their measures of immune function.”
“But it would also be interesting to get a more realistic sample of people who have more variable states of like disease and health,” she told MNT.
Additionally, Mengelkoch would like similar studies performed with older participants and a more racially diverse group of participants.
With this study, researchers focused on innate immunity, the defense system individuals have at birth. Mengelkoch told MNT it would be interesting to do a similar study, examining acquired immunity, immunity acquired by infection or vaccination. “So looking at using some different immune measures to kind of tap at different parts of people’s immune function would be fascinating too,” she said.
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