There’s a universal comfort in feeling the warmth of the sun on your skin, a natural uplifting feeling that seems to lift mood and promote a feeling of contentment. Beyond the sheer pleasantness, there’s a fascinating science behind why we feel so good when exposed to sunlight. It’s a complex interplay involving key hormones, vital vitamins, and our own unique biological responses.

The Sunny Side of Serotonin and Melatonin

Our mood, sleep, and overall well-being are heavily influenced by two crucial hormones: serotonin and melatonin. And exposure to sun and light plays a significant role in their day-to-day regulation

Serotonin, often dubbed the “feel-good” hormone, is a neurotransmitter that contributes to feelings of happiness, satisfaction and well-being. Exposure to bright light, especially sunlight, is known to boost serotonin production^{1 2}. This is why you might feel more energised and positive on a sunny day compared to a gloomy one. The retina in our eyes detects the light, sending signals to the brain to increase serotonin synthesis.

Conversely, melatonin is the hormone responsible for regulating our sleep-wake cycle. Its production is suppressed by light and stimulated by darkness. When the sun sets, melatonin levels naturally rise, signalling to our bodies that it’s time to sleep. Disruptions to this natural light-dark cycle, such as prolonged indoor living or artificial light exposure at night, can throw off melatonin production, leading to sleep disturbances³. Sunlight exposure during the day helps to “set” our internal clock, ensuring a robust melatonin surge at night, promoting better sleep.

Vitamin D: The Sunshine Vitamin and Seasonal Depression

While serotonin and melatonin are directly influenced by light, Vitamin D enters the scene as another critical player, synthesised in our skin upon exposure to ultraviolet B (UVB) rays from the sun. Often referred to as the “sunshine vitamin,” Vitamin D is vital for bone health, immune function, and increasingly, its role in mental wellbeing is gaining recognition.

One of the most compelling connections is between Vitamin D deficiency and Seasonal Affective Disorder (SAD), a type of depression that typically occurs during the fall and winter months when sunlight exposure is limited. Research suggests a link between lower Vitamin D levels and increased risk or severity of SAD symptoms, as well as an improvement in mood and depression from Vitamin D supplementation^{4 5}. While the exact mechanisms are still being fully understood, Vitamin D receptors are present in areas of the brain associated with mood regulation, and it’s thought to influence neurotransmitter synthesis and brain function⁶.

Bio-individuality in Vitamin D Synthesis: It’s Not One-Size-Fits-All

The amount of Vitamin D our bodies produce from sun exposure isn’t uniform. Several factors contribute to this fascinating bio-individuality:

• Season: The intensity of UVB rays varies significantly with the seasons. In Sydney, for example, the summer months (December-February) offer ample UVB, while winter months (June-August) have lower intensity, meaning less Vitamin D synthesis even with similar exposure times. Latitudinal differences are also critical; regions further from the equator experience less intense UVB year-round.
• Skin Tone: Melanin, the pigment responsible for skin color, acts as a natural sunscreen. Individuals with darker skin tones have higher melanin levels, which reduces the amount of UVB radiation that penetrates the skin. This means people with darker skin require longer sun exposure times to produce the same amount of Vitamin D as those with lighter skin.
• Sunscreen Use: Sunscreen, while crucial for protecting against skin cancer, effectively blocks UVB rays, thereby preventing Vitamin D synthesis. A sunscreen with an SPF of 15 can block approximately 93% of UVB rays, and higher SPFs block even more (Ramanathan et al., 2017). This presents a bit of a dilemma: protect your skin from sun damage, but potentially limit Vitamin D production. The key lies in balanced, sensible sun exposure.

A Naturopathic Approach to Sunlight & Mood

Given these factors, how can we harness the sun’s mood-boosting and health-promoting benefits responsibly?

• Smart Sun Exposure: Aim for short, regular periods of sun exposure, especially during peak UVB hours (generally mid-morning to late afternoon), without sunscreen on a small area of skin if appropriate for your skin type and location. In Sydney, this might mean 10-20 minutes a few times a week, but always to check UV index levels and expose your skin to the sun in periods that won’t causing burning.
• Know Your Skin: Understand how your skin reacts to the sun. If you have fair skin, you’ll burn much faster and need less time in direct sun for Vitamin D synthesis.
• Consider Supplements: Especially during winter months, or if you have darker skin or limited sun exposure, a Vitamin D supplement might be a wise choice. Consult with a healthcare professional to determine your Vitamin D levels and appropriate dosage.
• Prioritise Outdoor Time: Simply spending more time outdoors, even if not directly in the sun, can expose you to brighter ambient light, which still positively impacts serotonin and melatonin regulation.
• Regulate Light Exposure: Aim to view morning sunlight at the start of the day, and use dim warm lighting around the home at night time. This will help to regulate your circadian rhythm, serotonin and melatonin production.

If you are experiencing seasonal depression, low mood or recurrent illnesses then reach out. We can explore your pathology, nutrient levels, diet and lifestyle to understand and treat what’s driving your symptoms

References

1. Praschak-Rieder, N., & Willeit, M. (2012). Imaging of seasonal affective disorder and seasonality effects on serotonin and dopamine function in the human brain. Current topics in behavioral neurosciences, 11, 149–167. https://doi.org/10.1007/7854_2011_174 ↩︎
2. Cui, Y., Gong, Q., Huang, C., Guo, F., Li, W., Wang, Y., & Cheng, X. (2021). The relationship between sunlight exposure duration and depressive symptoms: A cross-sectional study on elderly Chinese women. PloS one, 16(7), e0254856. https://doi.org/10.1371/journal.pone.0254856 ↩︎
3. Raible, F., Takekata, H., & Tessmar-Raible, K. (2017). An Overview of Monthly Rhythms and Clocks. Frontiers in neurology, 8, 189. https://doi.org/10.3389/fneur.2017.00189 ↩︎
4. Roșian, A., Zdrîncă, M., Dobjanschi, L., Vicaș, L. G., Mureșan, M. E., Dindelegan, C. M., Platona, R. I., & Marian, E. (2025). The Role of Vitamin D in the Management of Major Depressive Disorder: A Systematic Review. Pharmaceuticals (Basel, Switzerland), 18(6), 792. https://doi.org/10.3390/ph18060792 ↩︎
5. Jorde, R., Sneve, M., Figenschau, Y., Svartberg, J., & Waterloo, K. (2008). Effects of vitamin D supplementation on symptoms of depression in overweight and obese subjects: randomized double blind trial. Journal of internal medicine, 264(6), 599–609. https://doi.org/10.1111/j.1365-2796.2008.02008.x ↩︎
6. Roșian, A., Zdrîncă, M., Dobjanschi, L., Vicaș, L. G., Mureșan, M. E., Dindelegan, C. M., Platona, R. I., & Marian, E. (2025). The Role of Vitamin D in the Management of Major Depressive Disorder: A Systematic Review. Pharmaceuticals (Basel, Switzerland), 18(6), 792. https://doi.org/10.3390/ph18060792 ↩︎