Researchers studied over 6,000 Chinese teenagers to understand why their moods change with the seasons. They found that winter brings the most depression and anxiety, mainly because of less sunlight and vitamin D deficiency. Spring stress from school exams affects sleep and emotions, while summer anxiety comes from social pressure and social media. The good news? Light therapy in winter and better support during stressful seasons can really help. This research shows that teenagers’ mental health isn’t just about one thing—it’s a mix of body chemistry, school stress, and social situations all working together.

The Quick Take

  • What they studied: How seasons affect teenage depression and anxiety, and what causes these seasonal mood changes
  • Who participated: 6,121 Chinese teenagers surveyed about their moods across different seasons, plus 1,000 teens tracked over time and 200 teens who tried light therapy
  • Key finding: Winter is the hardest season for teen mental health, with depression scores averaging 14.5 out of a possible higher score. This is mainly caused by less sunlight leading to vitamin D deficiency and increased stress from social situations
  • What it means for you: If you’re a teenager who feels sadder in winter, you’re not alone—it’s partly biology. Light therapy (sitting near special bright lights) and vitamin D supplements may help. Schools could also help by adjusting exam schedules and teaching students about healthy social media use during different seasons

The Research Details

This research used three different study methods to get a complete picture. First, researchers surveyed 6,121 teenagers at one point in time to see how their moods changed by season. Second, they followed 1,000 teenagers over several months to watch how their moods actually changed as seasons switched. Third, they gave 200 teenagers light therapy during winter and measured if it helped their depression. They measured depression using a questionnaire called PHQ-9, anxiety using GAD-7, and seasonal mood patterns using SADQ. They also tested blood levels of vitamin D and melatonin (a sleep hormone) to understand the biological side of seasonal mood changes.

Using multiple study methods is important because it shows the same pattern from different angles. The surveys show what’s happening, the tracking shows it happens over time, and the light therapy experiment shows that we can actually fix the problem. This combination makes the findings much more trustworthy than just one type of study alone.

This study is fairly strong because it included a large number of teenagers (over 6,000), used established mental health questionnaires that doctors use in real life, measured actual body chemicals like vitamin D, and tested whether a treatment actually works. However, the study only included Chinese teenagers, so results might be different in other countries. The light therapy group was smaller (200 people), which is normal for testing treatments.

What the Results Show

Winter was the worst season for teenage mental health. Depression scores averaged 14.5 (on a scale where higher numbers mean more depression), and this was strongly connected to low vitamin D levels. When vitamin D was low, depression was worse—for every unit drop in vitamin D, depression got noticeably worse. Spring brought a different problem: school exam stress affected how well teenagers slept and made them emotionally unstable, partly through changes in melatonin (the sleep hormone). Summer anxiety was different again—it was linked to feeling overwhelmed by social situations and unhappy with their bodies, possibly made worse by social media. The light therapy experiment showed real results: teenagers who used bright light therapy in winter had vitamin D levels increase by 8.2 units and their depression scores dropped by 3.1 points, which is meaningful improvement.

The research found that different seasons affect boys and girls somewhat differently, and that the problems change depending on whether teenagers were in middle school or high school. This suggests that one-size-fits-all solutions won’t work—teenagers need different help at different times of year and depending on their age and gender.

Previous research has shown that seasonal mood changes exist, but this study goes deeper by explaining exactly why it happens. It confirms that vitamin D deficiency in winter is a real problem for teens, and it adds new information about how spring exams and summer social stress each create their own mental health challenges. The light therapy results match what doctors have seen in adults with seasonal depression.

This study only included teenagers in China, so the results might be different in countries with different seasons, school systems, or cultures. The light therapy group was smaller than the survey group, so we’re less certain about those results. The study couldn’t prove that vitamin D deficiency directly causes depression—it just shows they happen together. Also, the study relied on teenagers answering questions about their moods, which might not be perfectly accurate.

The Bottom Line

Moderate confidence: Teenagers should get vitamin D supplements or more sunlight exposure in winter. Moderate confidence: Light therapy lamps can help reduce winter depression. Low to moderate confidence: Schools should consider flexible exam schedules in spring and teach social media literacy in summer. High confidence: Teenagers should be monitored for mood changes throughout the year, especially in winter.

This applies to teenagers, especially those who notice their mood gets worse in winter. Parents and school counselors should pay attention to these seasonal patterns. Teachers might use this to understand why some students struggle more at certain times of year. This is less relevant to adults or very young children, though some of the principles might apply.

Light therapy typically shows benefits within 3-7 days of regular use. Vitamin D supplements take 2-4 weeks to raise blood levels noticeably. Mood improvements usually follow within 2-4 weeks of vitamin D levels improving. For school-based interventions, benefits would likely show up within one school season.

Want to Apply This Research?

  • Track mood daily using a simple 1-10 scale, plus note vitamin D intake, sunlight exposure time, sleep hours, and academic stress level. Compare patterns across seasons to identify your personal seasonal mood trends.
  • Set a daily reminder to spend 15-30 minutes in bright light (either sunlight or a light therapy lamp) during winter months. Log this activity in the app and watch for mood improvements over 2-4 weeks.
  • Create a seasonal dashboard showing mood trends across all four seasons. Set alerts for when mood scores start dropping in your typical problem season (usually winter). Track vitamin D levels if possible, and correlate them with mood scores to see your personal pattern.

This research provides helpful information about seasonal patterns in teenage mental health, but it should not replace professional medical advice. If you or a teenager you know is experiencing depression, anxiety, or other mental health concerns, please talk to a doctor, school counselor, or mental health professional. Light therapy and vitamin D supplements may help, but they work best as part of a complete treatment plan guided by a healthcare provider. This study was conducted in China, so results may vary in other populations.