The Link Between Mood, Vitamin D, Sunlight and Your Body Clock

The Link Between Mood, Vitamin D, Sunlight, and Your Body Clock

If you’re feeling more tired, lethargic or low during the winter months, you’re not alone. There’s strong scientific evidence explaining how reduced sunlight exposure during winter can affect your energy, sleep, and mental health.

Vitamin D: More Than a Bone Nutrient

Vitamin D is commonly known for its role in bone health, but it also plays a crucial part in brain function, mental clarity, and emotional regulation. In fact, vitamin D behaves more like a hormone than a vitamin, influencing brain chemistry, mitochondrial function, and inflammatory processes, all of which are associated with mental health.

Low vitamin D levels are associated with:

• Depressed mood
• Fatigue and low motivation
• Poor concentration and brain fog
• Increased anxiety and irritability

Here’s How Vitamin D Supports Your Mental and Metabolic Health:

Vitamin D and Mood-Related Brain Chemistry

• Helps regulate serotonin and dopamine, which are essential for mood, motivation, and emotional balance
• Supports tryptophan hydroxylase, the enzyme involved in converting tryptophan into serotonin

 Vitamin D and Mitochondrial Function

• Supports the mitochondria (the energy-producing parts of your cells), particularly in brain cells, which require high energy to function properly
• Reduces oxidative stress, helping the brain use oxygen and nutrients more efficiently
• Supports energy metabolism, directly influencing mental clarity, drive, and resilience

Vitamin D and Inflammation

• Acts as an immune modulator, reducing chronic inflammation that can impair mood, cognition, and sleep
• Helps maintain healthy neuroimmune signalling, which is often disrupted in people with depression and other mood disorders

Why Sunlight Matters for Vitamin D (and Why the Skin Is Key)

Your body makes vitamin D naturally when your skin is exposed to ultraviolet B (UVB) rays from the sun. While supplements can be helpful when levels are low, the vitamin D your body produces through the skin is biologically active, tightly regulated, and integrated with your circadian rhythm.

In winter, especially in southern regions of Australia, the sun sits lower in the sky, and UVB exposure is significantly reduced. Even if you spend time outdoors, you’re unlikely to make enough vitamin D unless you’re outside at midday, when UVB levels are at their highest.

Skin-based vitamin D production is:

• Self-regulating: Your body makes only what it needs, reducing the risk of toxicity
• Synchronized with circadian function: Sunlight exposure through the skin and eyes reinforces your body clock, improving mood, hormone production, and sleep
• Biologically efficient: Endogenously produced vitamin D is more efficiently converted into its active form (calcitriol), which supports hormonal and immune balance across multiple systems—including the brain

There’s a reason we tend to associate a natural tan with vitality.  It often reflects real biological health. A light, sun-induced tan (not sunburn) suggests someone has:

• Spent time outdoors and produced vitamin D naturally
• Supported their circadian rhythm through regular sunlight exposure
• Benefited from improved mitochondrial function and reduced inflammation

Of course, sun safety matters. But brief, consistent periods of natural sunlight, particularly in winter, can be a powerful, low-cost way to support both mental and physical wellbeing.

Sunlight Timing Matters: UVA and UVB

Getting outside at the right times can help you support both your mood and your metabolic health.

• Early morning light exposure (mainly UVA) helps regulate your circadian rhythm, boost serotonin, and prime your body for melatonin release later in the evening
• Midday light exposure (when UVB is present) is essential for vitamin D production, especially in winter when your daily UVB window may be limited to a few hours

Even on cloudy days, being outside helps. Artificial indoor light simply doesn’t have the same biological impact on your brain and body. And exposure to artificial light at night can significantly disrupt your circadian rhythms and mental health.

Practical Ways to Support Your Mood and Brain in Winter

Here are a few simple, evidence-based strategies you can start using right away:

Get outside in the morning

• Aim for 15–30 minutes of natural light within 1–2 hours of waking
• This supports your serotonin production and anchors your circadian rhythm

Get midday sunlight exposure

• Try to get direct sunlight on bare skin around midday, especially in winter
• This is the best time for vitamin D synthesis when UVB is present
• If you’re not getting enough sun, speak to your GP about a vitamin D test

Keep your sleep schedule consistent

• Go to bed and wake up at roughly the same time every day
• Reduce screen use and bright lights at night to support natural melatonin production

Align your meals with your body clock

• Eat earlier in the day and avoid large meals at night
• Include nutrient-dense foods to support brain energy and stabilise blood sugar

Move your body regularly

• Outdoor movement is ideal for mood, light exposure, and mitochondrial health
• Even a short walk can improve circulation and reduce stress

If you’re not feeling like yourself this winter, there may be a biological explanation. Reduced sunlight exposure, low vitamin D, disrupted circadian rhythms, and reduced mitochondrial energy can all impact your mental health.

These are modifiable factors.

By reconnecting with natural light, prioritising midday sun exposure, supporting vitamin D levels, and aligning your routine with your body’s internal clock, you can begin to restore your energy, improve mood stability, and support your brain’s full potential.

By gently supporting your circadian rhythm, checking your vitamin D, and prioritising natural light, you can improve your mood, energy, and mental clarity.