Special report Plenty of fruit, nature, sun and sleep will make next year more enjoyable finds NZ study.
If your New Year resolution is to be happier, make your priorities fruit, nature, sun and sleep.
That's according to the results so far of a sprawling New Zealand study that has tracked nearly 1500 young people to learn what makes for a happy life.
The Daily Life Study, overseen by Otago University psychologist Dr Tamlin Conner, has produced five major papers since the research project began in 2011.
The latest has found that levels of selenium - typically gained from bread, fish, poultry and eggs - can place young people at greater risk of depression if they are too high, or worse, too low.
Dr Conner said the overall aim of the project had been to pinpoint the factors that influenced wellbeing, and these had ranged from personality traits, genetics, exercise and time spent outside.
"It's a grand, comprehensive investigation into the daily lives of young adults' wellbeing."
Each of the student participants, all aged between 18-25, were closely monitored over periods of two weeks as they went about their lives.
After providing detailed information about themselves on the first day, their moods were tracked by sending them text messages asking them to grade how motivated, positive, energetic, negative and tense they felt on a scale of one to nine.
The pursuit of happiness
•Fruit and veges: Healthy amounts can elevate moods and raise curiosity and creativity.
At the end of each day, they completed an online daily diary asking them a much larger set of questions about their wellbeing that day and variables, such as sleep the night before, exercise, and food and alcohol consumed.
Completing the study period, they provided a blood sample, filled out more questionnaires, and were measured for height, weight and body fat composition.
In total, 997 women and 485 men took part, with an average age of 19 years.
Dr Conner said many of the findings had been surprising, but others less so.
"Young adults' wellbeing is strongly tied to healthy habits - things that young adults might not think are emotion-related."
When they slept, ate well and exercised regularly, they were better able to regulate their emotions.
"Establishing healthy habits during young adulthood can last a lifetime."
Those who consumed none or just one serving of fruit and vegetables each day, for example, reported the lowest average positive mood.
"People also felt better on days they eat more fruits and vegetables, and the causal direction seems to be that fruit and vegetables influence mood, not the other way around."
It was also found to be related to higher curiosity and creativity, with the participants reporting feeling more engaged and interested after eating the healthy foods.
As greater curiosity was a trait that predicted greater wellbeing and successful ageing, it was possible that diet brings the young people better engagement and zest for life for the rest of their years.
But the researchers had been left worried by the "rampant" level of depression found among the students.
Among the 978 who contributed to the selenium study, just over one third scored at levels indicating significant levels of depressive symptoms.
"This is a big concern that needs to be addressed," said Dr Conner, who is now helping the university find mobile-based approaches to improve wellbeing for the students.
The project had also found spending time in nature was good for the soul - even a walk through the botanic gardens improved emotions.
Selenium key depression defence
A key mineral in bread, fish, poultry and eggs can affect a young person's mood if intake is too high or low.
The most recent research paper from Otago University's Daily Life Study found a link between selenium concentration and a negative mood among young adults. Results from a sample of 978 young people found that those with unbalanced levels of selenium had the highest risk of depressive symptoms, especially if concentrations were too low.
Lead researcher Dr Tamlin Conner said adequate selenium intake was required for optimal antioxidant defences to protect body tissues from oxidative damage through glutathione peroxidise, a key antioxidant enzyme.
"Although we did not test the physiological mechanisms, other research shows that oxidative damage to the brain and nervous system contributes to the development of depression."
The main source of selenium in the New Zealand diet is bread, followed by fish and seafood, then poultry, and eggs. New Zealand has a well-known history of low selenium intake.