Skip to main content

Verified by Psychology Today


We Had Joy, We Had Fun: We Really Feel Better in the Summer

Diet and mood seem to be influenced through the serotonin / melatonin cycle.

Key points

  • Mood and dietary choices appear to vary between summer and fall.
  • The variance might be influenced by length of day and due to the serotonin/melatonin cycle.
  • When fall arrives, get out in the light as much as you can to influence the serotonin / melatonin cycle in your favour. 
Hassan Ouajbir/Pexels
Seasonal changes underly reports of wellbeing in complex ways
Source: Hassan Ouajbir/Pexels

We know that sleep, diet and exercise all play a part in our mental wellbeing. We also know that this relationship is complex: these modifiable factors are intertwined so that a change in one might lead to changes in another, leading to different outcomes. For example, a poor night’s sleep might mean that you’re awake for a greater number of hours, and have more opportunity to eat. You might also seek sugary or comfort foods you associate with a quick energy hit to pep you up in the short-term. The problem is that there is often a rebound meaning that although you feel better in the short-term, you might not feel so good over a longer period.

Circadian rhythms underpin mood changes?

But you can also consider these modifiable factors as an overlay against seasonal changes associated with light-induced alterations in our circadian rhythms. We know that seasonal changes that affect length of days change our mood through altering our brain chemistry. But the complex multidimensional nature of the relationship between diet, sleep, exercise and seasonal variations and how they are linked to changes in mentality health and wellbeing is multidimensional and incompletely understood.

In what appears to be one of the first studies to shine a light on these dynamics, a diary study carried out at the University of Binghampton studied 52 adults over a 4-week period, collecting daily records of dietary intake, sleep quality, exercise frequency and mental distress, from June through to December.

The study discovered that mental distress was indeed a complex interplay involving all factors that were measured, but that improving one factor (diet, exercise, or sleep) tended to be associated with improvements in other inputs to mental distress experienced too. This has interesting implications: for example, if it feels hard to change diet or exercise frequency, the simplest place to start might be getting better quality sleep. Increased energy and experience of quality rest and sleep might then make it easier to increase exercise variety and frequency, which drives better sleep, and more healthy diet choices. The study results imply it could start a virtuous circle, with any programme intervention starting with the easiest factor to change.

In particular, they found reports gathered in summer were linked to better overall mood and diet quality than those taken in the fall.

The serotonin/melatonin cycle

There are lots of ways in which changes in length of day might influence our moods, including through modifying serotonin levels. Serotonin is the key hormone that stabilizes our mood, feelings of well-being, and happiness. The study authors argue that shorter daylight hours lead to increased melatonin production at the expense of serotonin. Interestingly, melatonin production surges during periods of the year with shorter days and declines in the summer when days are longer.

Alterations in serotonin levels also influence feeding behaviour, with knock-on effects on both diet quality and mood. And because an imbalanced diet also affects the serotonin / melatonin cycle, this then contributes to an alternative descending and potentially vicious spiral of low mood and poor quality diet when days are shorter.

Diet, sleep and exercise all contribute to our mental wellbeing. But it seems likely that there are seasonal variations in how this relationship plays out that we need to pay attention to. Whereas summer may improve our mood and lead us to make choices in modifiable lifestyle factors that improve our wellbeing, shorter days in the fall and winter may lead to lower mood and influence our dietary habits such that we may be prone to fall into habits that combine to decrease our sense of wellbeing.

Enjoy the summer months and prepare for the fall. When it arrives, get out in the light as much as you can to influence the serotonin / melatonin cycle in your favour.


Lina Begdache, Mei-Hsiu Chen, Casey E. McKenna, Dylan F. Witt (2021). Dynamic associations between daily alternate healthy eating index, exercise, sleep, seasonal change and mental distress among young and mature men and women, Journal of Affective Disorders Reports, Volume 5,