If your mood, energy, or motivation dips as the days shorten, you are far from alone. Here is what the research says about vitamin D and light.
Every year around this time, many people notice the same shift: getting out of bed feels harder, cravings change, and the usual spark fades along with the daylight. For some, it is a mild seasonal slump. For others, it is a recurring pattern of low mood that clinicians call seasonal affective disorder (SAD). Either way, it is worth understanding what actually helps, and what is more hype than evidence.
Why a fall mood dip happens
Shorter days change the light signals your brain uses to set its internal clock. Researchers believe this can disrupt sleep timing, alter serotonin and melatonin signalling, and shift daily rhythms in ways that affect mood and energy. In Canada, the sun sits low enough through the fall and winter that our skin makes very little vitamin D from sunlight between roughly October and March, which is one reason vitamin D gets so much attention at this time of year.
Common signs of a seasonal pattern include low energy, oversleeping, craving carbohydrates, difficulty concentrating, and pulling away from social plans. If these symptoms return each year and interfere with daily life, it is a good reason to check in with a health professional rather than simply pushing through.
What the evidence says about vitamin D
It is tempting to assume that vitamin D is the answer, but the research is more nuanced. Low vitamin D levels are common in northern climates and have been linked with low mood in observational studies. However, clinical trials testing vitamin D as a treatment for seasonal or general depression have produced mixed and often modest results, and it has not been shown to be a reliable stand-alone treatment for SAD.
That does not mean vitamin D is unimportant. It plays a role in bone health, immune function, and muscle function, and many Canadians do not get enough through diet alone. The practical approach is to find out where you stand rather than guess. A blood test can measure your level, and a licensed practitioner can help you decide whether supplementation makes sense and at what dose. More is not better: vitamin D is fat-soluble, and high doses taken without guidance can cause problems.
Approaches with stronger support
For seasonal patterns of low mood, a few strategies have a better evidence base than any single supplement:
- Bright light therapy. Using a light box that delivers about 10,000 lux for roughly 20 to 30 minutes soon after waking is one of the most studied non-drug options for SAD. Eye safety matters, so check with a practitioner first if you have eye conditions or bipolar disorder.
- Morning daylight and movement. A brisk walk outside within an hour or two of waking supports your body clock, even on overcast days, when outdoor light is still far brighter than indoor lighting.
- Psychotherapy. Cognitive behavioural therapy adapted for SAD has shown benefits that can last beyond a single season.
- Consistent sleep, meals, and social contact. Regular routines help stabilize mood when daylight is unreliable.
A naturopathic approach looks at these pieces together: lab testing where appropriate, nutrition, sleep, stress, and a realistic plan you can maintain. You can read more about how our practitioners support this on our mood and mental wellness naturopathic care page.
When to reach out for support
Feeling a bit flat in October is common, but persistent low mood, loss of interest in things you usually enjoy, or feeling hopeless deserves attention. If you are ever having thoughts of harming yourself, please contact the 9-8-8 Suicide Crisis Helpline (call or text 9-8-8 in Canada) or your local emergency services right away.
Seasonal changes are predictable, which means you can plan for them. Starting supports in early fall, before the darkest months arrive, tends to be easier than trying to recover once you are already struggling.
If you would like a personalized plan for the months ahead, we would be glad to help. Book a session at kurated.ca to talk with one of our practitioners about mood, energy, and seasonal wellness. This article is for general education and is not a substitute for individualized medical advice.