Progress Daily

Since 1948 three generations of residents in Framingham have participated in regular medical examinations. A new study (”Alone in the crowd: The structure and spread of loneliness in a large social network”; .pdf file here) by John Cacioppo that uses Framingham to analyse loneliness has found that it spreads very much like a communicable disease.

Participants in the study were routinely asked to list people who would probably know their whereabouts in the next 2 to 4 years, & were asked to describe their relationship with each person as friend, spouse, sibling, neighbour or colleague. Between 1983 and 2001 participants were regularly asked to state how many days a week they felt certain feelings, such as loneliness.

Analyzing this data, the researchers found that loneliness formed in clusters of people, and that once one person in a social network started expressing feelings of loneliness, others within the same network would start to feel the same way. Those who had immediate contact with lonely people were around 50% more likely than average to feel lonely themselves. In people who knew people who had direct contact with lonely people, the figure was 25%. Those with three degrees of separation showed roughly a 10% increase.

The effects were more noticeable among friends than family, and stronger among women than men.

“Alone in the crowd,” The Economist

Research by Emma Cohen (”Rowers’ high: behavioural synchrony is correlated with elevated pain thresholds“), suggests that training in a synchronised group may heighten tolerance for pain, & allow people to train longer.

The researchers got 12 members of Oxford’s heavyweight squad to row on machines in four 45-minute sessions over two weeks. In two sessions they rowed in complete isolation and in the others in groups of six, perfectly synchronised. Immediately following each session they deduced pain tolerance by gradually tightening a cuff around each rower’s arm. When he said “now” they stopped squeezing and noted the pressure.

The rowers’ pain thresholds were significantly higher following the group sessions. This was despite nearly identical power outputs in all four tests and efforts to control for possible confounding variables, such as the time of day.

“Fitter with friends,” The Economist

Girls who grow up without their fathers at home reach sexual maturity earlier than girls whose fathers live with them (and early-bloomers are more likely to suffer depression, hate their bodies, engage in risky sex and get pregnant in their teen years).

Research by Jane Mendle (”Associations Between Father Absence and Age of First Sexual Intercourse“) suggests heredity is the cause: the genes that make a dad more likely to leave his family also cause early sexual development.

The researchers analyzed data American National Longitudinal Survey of Youth data on 1,400 boys and girls, each of whom was related to at least one other subject through their mother. Most of the mothers were pairs of sisters, but some were identical twins or first cousins raised as sisters.

The more closely related the cousins were — by having mothers who were identical twins, for instance, versus cousins — the closer their age at first sexual experience, regardless of whether or not a father lived in the home.

“Daddy’s girl,” The Economist

In a study just published in Evolution and Human Behavior (”Costs and benefits of fat-free muscle mass in men: relationship to mating success, dietary requirements, and native immunity“), Steven Gaulin analyzes muscularity.

The data came from the NHNES, which followed 12,000 American men and women over the course of 6 years. The researchers found that men require 50% more calories than women do, even after adjusting for activity levels, and that their muscle mass is the strongest predictor of their intake of calories — stronger than their occupation or their body-mass index. Men’s immune systems are less effective than those of women (which was known before), and become worse the more muscular the men are (which was not).

The more muscular a man, the more sexual partners he reported, both in the past year and over his lifetime, and the earlier his first sexual experience was likely to have been.

Gaulin speculates that an evolutionary fight is going on between natural selection, which conserves metabolic expenditure and promotes longevity, and sexual selection, which willingly trades both for extra mating opportunities. This may explain why men have such a range of muscularity. In the past, the strong man would have had better mating opportunities in the short term, but the skinny guy who outlived him could have had just as much reproductive success over the course of his longer life.

“Mr Muscle,” The Economist

In most species, improved circumstances increase reproductive effort, yet as economic development gets going, country after country has experienced the “demographic transition,” in which fertility (the number of children borne by a woman over her lifetime) drops from around 8 to one-and-a-half.

Unless trends change, by the middle of the century, populations in the most developed countries will have shrunk and the number of retired individuals supported by each person of working age will increase significantly.

A study by Mikko Myrskyla, Hans-Peter Kohler, & Francesco Billari (”Advances in development reverse fertility declines“) suggests that the trend may change: as development continues, the demographic transition goes into reverse.

The researchers looked at two years 1975 and 2005, and analyzed countries using two factors, total fertility rate (the number of children that would be born to a woman in a particular country over the course of her life if she experienced the age-specific fertility rates observed in that country during the calendar year in question) and human development index or “HDI” (a measure used by the UN that includes life expectancy, average income per person, and level of education), which has a maximum possible value of one.

In 1975, of the 107 countries analyzed, the best was Canada, with an HDI of 0.89. By 2005, two dozen countries (of 240 analzyed) had HDIs above nine. In 1975, a graph plotting fertility rate against the HDI fell as the HDI rose. By 2005, though, once the HDI rose above 0.9 or so, it turned up, producing a “J-shaped” curve (the mirror image of a letter J).

In many countries with very high levels of development (around 0.95) fertility rates are now approaching two children per woman.

The nadir of fertility appears to be 1.3 children per woman but this new data suggests the ultimate outcome of development may be zero population growth.

“The best of all possible worlds?,” The Economist

Toxoplasma gondii is a parasite that lives in the guts of cats, where it sheds eggs in cat feces that are often eaten by rats. The parasites increase their odds of getting back to cats by changing the infected rats’ brains, making them less scared of cats (and so more likely to be eaten).

A new study by Jaroslav Flegr, Jan Havlíček, et. al, (”Increased incidence of traffic accidents in Toxoplasma-infected military drivers and protective effect RhD molecule revealed by a large-scale prospective cohort study“) found that subjects with high titers of anti-Toxoplasma antibodies had a probability of a traffic accident (17%) more than 6 times higher than Toxoplasma-free subjects.

“The Return of the Puppet Masters,” by Alex Tabarrok

Two years ago, a study by Carsten Wrosch (”You’ve Gotta Know When to Fold ‘Em: Goal Disengagement and Systemic Inflammation in Adolescence“) demonstrated the importance of giving up inappropriate goals — those teenagers who were better at doing so had a lower concentration of C-reactive protein, a substance (made in response to inflammation and) associated with an elevated risk of diabetes and cardiovascular disease.

A recent study by Dr Wrosch and Gregory Miller (”Depressive symptoms can be useful: Self-regulatory and emotional benefits of dysphoric mood in adolescence“) measured the “goal adjustment capacities” of 97 girls aged 15-19 over the course of 19 months. They asked the participants questions about their ability to disengage from unattainable goals and to re-engage with new goals.They also asked about a range of symptoms associated with depression, and tracked how these changed over the course of the study.

Those who experienced mild depressive symptoms could disengage more easily from unreachable goals. They also proved less likely to suffer more serious depression in the long run.

The prevalence of inappropriately optimistic persistence may help explain why the US has the highest depression rate in the world.

“Mild and bitter,” The Economist

Angus Maddison has estimated that life expectancy during the first millennium AD averaged about 25 years (lots of children died very young and many of the rest survived to middle age). Many more children survived into adulthood after the Industrial Revolution and by the beginning of the 20th century average life expectancy in America and the better-off parts of Europe was close to 50. By mid-century the gains from lower child mortality had mainly run their course & the extra years were coming from higher survival rates among older people. The UN thinks that life expectancy at birth worldwide will go up from 68 years at present to 76 by 2050 and in rich countries from 77 to 83 (women generally live 5-6 years longer than men).

Jim Oeppen and James Vaupel have charted life expectancy since 1840 (”Enhanced: Broken Limits to Life Expectancy“), joining up the figures for whatever country was holding the longevity record at the time, and found that the resulting trend line has been moving upward by about 3 months a year.

In the US, centenarians are the fastest-growing section of the population, with an increase from 3,700 in 1940 to over 100,000 now.

According to Robert Fogel, Western people’s average body size has increased by 50% over the past 250 years. And larger body size is correlated with better health and longer life.

“A world of Methuselahs,” The Economist

Martin Gibala had a group of college students, who were healthy but not athletes, ride a stationary bike at a sustainable pace for between 90 and 120 minutes. Another set of students grunted through a series of short, strenuous intervals: 20 to 30 seconds of cycling at the highest intensity the riders could stand. After resting for 4 minutes, the students pedaled hard again for another 20 to 30 seconds, repeating the cycle 4-6 times (depending on how much each person could stand), for a total of 2-3 minutes of intense exercise per training session.

Each of the groups exercised 3 times a week. After 2 weeks, both groups showed almost identical increases in their endurance (as measured in a stationary bicycle time trial), even though one group had exercised for 6-9 minutes per week, and the other about 5 hours. Additionally, molecular changes that signal increased fitness (such as increased volume of muscular mitochondria) were evident equally in both groups. The short, intense workouts aided in weight loss, too; the rate of energy expenditure remained higher longer into recovery after brief, high-intensity exercise than after longer, easier workouts. (Other researchers have found that intense, brief sessions of exercise improve cardiac health, even among people with heart disease.)

“Can You Get Fit in Six Minutes a Week?,” by Gretchen Reynolds

A 10-year Australian study (”Effect of social networks on 10 year survival in very old Australians“) found that older people with a large circle of friends were 22% less likely to die during the study period than those with fewer friends.

A large 2007 study (”The Spread of Obesity in a Large Social Network over 32 Years“) showed an increase of nearly 60% in the risk for obesity among people whose friends gained weight.

In 2008, Harvard researchers reported that strong social ties could promote brain health as we age (”Effects of Social Integration on Preserving Memory Function in a Nationally Representative US Elderly Population“). Over a 6-year period, memory among the least integrated declined at twice the rate as among the most integrated.

In 2006, a study (”Social Networks, Social Support, and Survival After Breast Cancer Diagnosis“) of nearly 3,000 nurses with breast cancer found that women without close friends were four times as likely to die from the disease as women with 10 or more friends. Proximity and the amount of contact with a friend wasn’t associated with survival, nor was having a spouse.

In 2008, researchers studied 34 college students (”Social support and the perception of geographical slant“), taking them to the base of a steep hill and fitting them with a weighted backpack. They were then asked to estimate the steepness of the hill. Some participants stood next to friends during the exercise, while others were alone. The students who stood with friends gave lower estimates of the steepness of the hill. And the longer the friends had known each other, the less steep the hill appeared.

“What Are Friends For? A Longer Life,” by Tara Parker-Pope