As the days grow shorter and sunlight becomes scarce, many women notice changes in energy, focus, and emotional balance. This seasonal shift is not simply psychological; it is biochemical. Hormones and neurotransmitters respond directly to light exposure, and the changes that occur through the fall and winter months can strongly influence mood, sleep, and overall well-being.
Understanding the Winter Hormone Shift
In Canada, daylight hours decrease significantly between October and February. This reduction in natural light affects production of serotonin, the neurotransmitter that helps regulate mood and calm the nervous system. Less sunlight means lower serotonin activity and often a dip in energy or motivation.
For women, these changes also interact with estrogen levels, which help regulate serotonin receptors in the brain. When estrogen levels fluctuate through the menstrual cycle, perimenopause, or menopause, serotonin balance may shift as well. This helps explain why many women experience more pronounced mood changes in winter, often referred to as Seasonal Affective Disorder (SAD).
The Serotonin-Estrogen Connection
Estrogen supports the synthesis and uptake of serotonin in several key brain regions related to mood and decision-making. When estrogen declines, serotonin function may drop, increasing the likelihood of anxiety, irritability, or fatigue.
Studies from the Canadian Journal of Psychiatry and McGill University’s Division of Women’s Health Research show that women with lower mid-cycle estrogen tend to have lower serotonin levels and greater seasonal mood variability. These findings highlight the importance of hormonal balance in maintaining emotional health during darker months.
Practical Steps for Balance
- Maximize Natural Light: Spend at least 20 minutes outdoors daily, even on cloudy days. Daylight stimulates serotonin and supports healthy sleep.
- Consider Light Therapy: Full-spectrum light boxes or dawn-simulating lamps can restore circadian rhythm and lift energy. Evidence from the Canadian Network for Mood and Anxiety Treatments (CANMAT) supports light therapy as a first-line option for SAD.
- Support Hormone Health Through Nutrition: Vitamin D, B6, and omega-3s play key roles in serotonin synthesis. Include fish, eggs, leafy greens, and fortified plant milks regularly.
- Movement and Stress Regulation: Moderate daily activity such as walking, yoga, or resistance training helps normalize cortisol, another hormone that interacts with serotonin.
- Testing and Personalized Care: Functional hormone testing can reveal how estrogen fluctuations may be affecting mood, allowing for targeted nutrition and supplementation.
When to Seek Support
If mood changes persist for more than two weeks or begin to affect sleep, appetite, or motivation, it may be time to speak with your naturopathic doctor. Functional medicine can help identify whether symptoms are linked to light exposure, hormone fluctuations, nutrient deficiencies, or other root causes.
The Takeaway
Winter can challenge both mood and motivation, but it also offers an opportunity to listen to the body’s natural rhythms. Understanding how serotonin and estrogen interact allows women to take preventive steps before symptoms escalate. With balanced attention to light, nutrition, and hormone support, it is possible to maintain steadiness and vitality through the season.
Evidence Sources
- Canadian Journal of Psychiatry (2024): “Light Exposure, Estrogen Fluctuation, and Seasonal Mood Disorders”
- McGill University Division of Women’s Health Research (2023): “Hormone–Neurotransmitter Interactions in Women’s Mood Regulation”
- CANMAT Guidelines (2024): “Evidence-Based Treatments for Seasonal Affective Disorder in Canada”
- Health Canada (2025): “Vitamin D and Serotonin Pathways in Mood Health”