Excessive sedentary screen time for toddlers has long been discouraged by health authorities because of its potential to disrupt sleep and decrease physical activity. The American Academy of Pediatrics, for example, recommends no screen time for children under 18 months and a max of one hour per weekday for children aged 2–5. But does that go far enough? Studies in recent years have suggested too much early screen time can also affect cognitive and language development, and now a major study from the University of Yamanashi involving 84,030 children in Japan has linked TV/DVD screen time to increased risk of autism in boys—but only in boys. The study showed children who watched between 2–4 hours per day of television and DVDs at one year of age were almost three times more likely to be diagnosed with autism at age three. Among girls there was no association. Given the ubiquity of devices in modern life, new guidance on how much screen time is appropriate in infancy is needed, the researchers write. JAMA Pediatrics

Do people genetically inherit their love for natural outdoor green spaces, or is that something we learn through exposure? Apparently it’s both. A new study by investigators at the National University of Singapore looking at a mix of 2,306 identical and non-identical twins in the United Kingdom found positive correlations between genetics and how often or how long people spend in public green spaces or domestic gardens. This is the first evidence of genes influencing our human disposition toward nature, though the study showed genes don’t completely dominate the picture. There was no correlation between shared identical genes and the level of urbanization in people’s neighborhoods, for instance. PLOS Biology

Similarities in orientation toward nature between identical “monozygotic” twin pairs and non-identical “dizygotic” twins. Chia-chen Chang/NUS

A pair of papers this week from researchers at the University of Innsbruck in Austria showed how a simple cervical screen could be used to identify women with increased risk of ovarian or breast cancer. In the first study, the researchers analyzed “epigenetic” DNA methylation changes to cervical cells, which were collected through a routine cervical smear. Looking at cell samples taken from 242 women with ovarian cancer and 869 women who were cancer-free, they identified a molecular pattern that allowed them to identify 71 percent of the women under 50 and 55 percent of the women over 50 years who had ovarian cancer. In a second paper, they looked at cervical smears from 329 women with breast cancer and 869 women without and by looking at epigenetic changes to the cervical cells, they created a tool dubbed Women’s risk IDentification for Breast Cancer index (WID-BC-index) to help identify women at risk of breast cancer. Nature Communications

Researchers at the University of Queensland in Brisbane, Australia, Southern University of Science and Technology in Shenzhen, China, and Dresden University of Technology in Germany have proposed a new mechanism that links exercise to the generation of new neurons in the adult hippocampus—a brain region crucial for learning and memory. While exercise has long been known to induce plasticity in this region, nobody understood how. But by studying genetically modified mice, the researchers showed the neurogenesis-enhancing effect of exercise is linked to a protein called selenoprotein P (SEPP1), which transports selenium, a trace mineral found naturally in soil and added to many multivitamin supplements. They also showed that giving dietary selenium to mice with injured hippocampi restored the proliferation of neurons there and reversed age-related cognitive decline. Cell Metabolism

A provocative new study involving thousands of 30–75 year-old adults in Canada and Poland shows that excess body fat and its distribution in the belly are associated with lower cognitive scores. The study pulled 9,189 subjects from two larger cohorts—the Canadian Alliance for Healthy Hearts and Minds (CAHHM) and the Prospective Urban Rural Epidemiological-Mind (PURE-MIND). It found that people who have a higher percentage of body fat overall and who carry more “spare tire” visceral adipose tissue in their abdomens had more cardiovascular risk factors, suffered from more vascular brain injuries, and had overall lower cognitive scores. Strategies that prevent or reduce fat may preserve cognitive function, write researchers at McMaster University in Ontario, Canada, who led the study. JAMA Network Open