If you’ve been waking up tired, reaching for coffee by 10 a.m., and dragging through your afternoons with no energy - your first thought might be: I need more sleep. But what if your fatigue has less to do with how long you sleep and more to do with how well your cells are functioning? Enter: Vitamin D. 

Known as the ‘sunshine vitamin,’ it plays a far bigger role in your energy levels than most people realise. And in today’s indoor, screen-heavy world, deficiency is incredibly common - even during summer.

1. Vitamin D Is a Mitochondrial Must-Have

Vitamin D doesn’t just support bone health and immunity, it’s essential for mitochondrial function. Your mitochondria are the energy factories inside your cells, producing ATP (adenosine triphosphate), which powers everything from muscle movement to brain activity.

Low vitamin D levels have been shown to impair mitochondrial oxidative capacity, which reduces the energy your cells can generate [1]. Translation? Less energy on a cellular level = less energy in your body.

2. It Balances Hormones That Regulate Fatigue

Vitamin D is a hormone precursor, meaning it’s involved in the synthesis and regulation of other hormones like testosterone, oestrogen, and thyroid hormones - all of which influence energy, metabolism, and mood [2]. A deficiency can throw your hormonal balance out of sync, leading to fatigue that doesn’t improve with rest.

Women, in particular, may notice more pronounced effects during hormonal transitions like perimenopause or postpartum when vitamin D demands are higher.

3. It Supports Mood, And Mood Affects Energy

There’s a strong link between low vitamin D and depression, particularly seasonal affective disorder (SAD), which is often marked by fatigue, brain fog, and apathy [3]. While mood and energy are distinct, they are deeply intertwined. When your outlook is low, your energy tends to follow.

Supplementing with vitamin D in deficient individuals has been shown to improve depressive symptoms, and with it, restore some mental and physical energy [4].

4. It Modulates Inflammation, A Hidden Drain on Energy

Chronic, low-grade inflammation is one of the most silent and insidious causes of fatigue. It disrupts normal cellular function, stresses the immune system, and diverts energy from your day-to-day needs to ongoing repair processes.

Vitamin D helps regulate the immune system and suppress pro-inflammatory cytokines [5]. This reduces the inflammatory burden on the body and can free up much-needed energy for movement, cognition, and vitality.

5. You May Not Be Getting Enough (Even in Summer)

Despite longer days and brighter skies, many people are still vitamin D deficient. Sunscreen, indoor jobs, darker skin tones, and poor absorption all reduce how much vitamin D your body can synthesise from the sun [6]. Blood testing is the only way to know your true status, but general signs include fatigue, low mood, frequent illness, and muscle weakness.

The Bottom Line

If you’re feeling chronically drained, don’t just look at your sleep hygiene or caffeine intake. Think broader, think cellular. Vitamin D is a foundational nutrient that influences energy from multiple angles: hormone balance, inflammation, mitochondrial power, and mood.

Optimising your levels could be the missing piece in your energy puzzle. Sometimes, the fix isn’t more rest, it’s better nutrients.

Call us on 02476363873 or email us at hello@madebydaily.com to discuss your questions with a member of our clinical team.

Enjoyed this guide? Now read…

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Perimenopause or Just Tired? How to Spot the Subtle Signs

References

 1. Sinha, A. et al. (2013). Improved mitochondrial oxidative capacity and muscle function following vitamin D supplementation in older adults. J Clin Endocrinol Metab.
2.  Holick, M. F. (2007). Vitamin D deficiency. N Engl J Med.
3.  Melrose, S. (2015). Seasonal affective disorder: An overview of assessment and treatment approaches. Depression Research and Treatment.
4. Shaffer, J. A. et al. (2014). Vitamin D supplementation for depressive symptoms: a systematic review and meta-analysis of randomized controlled trials. Psychosomatic Medicine.
5. Aranow, C. (2011). Vitamin D and the immune system. J Investig Med.
6. Forrest, K. Y. Z., & Stuhldreher, W. L. (2011). Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res.