When the clocks go back and the days get darker, most of us feel the drop — in temperature, energy, and motivation. But there’s something else that takes a big hit: your body’s Vitamin D levels.

Unlike other nutrients, Vitamin D isn’t found in abundance in food. We make most of it through sunlight hitting our skin. But between October and March in the UK, that simply doesn’t happen — the sun’s UV rays aren’t strong enough to trigger Vitamin D production.

That’s why Public Health England recommends everyone consider a daily Vitamin D supplement through autumn and winter. For anyone who trains regularly or spends their days indoors, it’s a no-brainer.

Why Vitamin D Matters So Much

A study titled ‘Vitamin D: Evidence-Based Health Benefits and Recommendations for Population Guidelines’ published in 2025 concluded…

‘Serum concentrations > 30 ng/mL (75 nmol/L) significantly lower disease and mortality risks compared to <20 ng/mL. With 25% of the U.S. population and 60% of Central Europeans having levels <20 ng/mL, concentrations should be raised above 30 ng/mL. This is achievable through daily supplementation with 2000 IU/day (50 mcg/day) of vitamin D3, which prevents diseases and deaths.’

In English, this says that significant amounts of the population suffer from low vitamin D levels, which translates to potential health risks. With additional supplementation, many of these risks can be reduced or avoided.

Here’s how vitamin D supplementation helps to improve health markers…

1. Supports your immune system

Colds, flu and general winter bugs thrive when your immune system is under pressure. Vitamin D helps regulate immune responses and keep defences strong — crucial when you’re training hard and need your body to recover efficiently.

2. Keeps bones strong and healthy

Vitamin D works hand-in-hand with calcium, ensuring it’s absorbed properly to build and maintain bone strength. Without enough, bones can become weaker over time — a particular issue for older adults or anyone lifting heavy in the gym.

3. Aids muscle function and recovery

Low Vitamin D levels are linked with reduced muscle strength and slower recovery. By keeping levels topped up, you support better performance, endurance, and overall training output — especially useful during the colder months when energy naturally dips.

4. Helps beat the ‘winter blues’

Ever noticed your mood takes a knock when the sunlight disappears? That’s no coincidence. Vitamin D plays a role in brain chemistry, including the regulation of serotonin, one of the key hormones linked to happiness and motivation.

How to Supplement Vitamin D Effectively

  • The standard dose: Most people benefit from 10 micrograms (400 IU) of Vitamin D daily through autumn and winter.

  • Active individuals: If you train hard or spend very little time outdoors, you might need a higher dose — always check with a GP or nutrition professional first.

  • Pair it with Vitamin K2: These two nutrients work brilliantly together — Vitamin D helps you absorb calcium, while K2 directs it to your bones (not your arteries).

  • Take it with food: It’s a fat-soluble vitamin, so it’s best absorbed alongside a meal containing healthy fats — think eggs, avocado, salmon or nuts.

The Bottom Line

If you’re putting in hours at the gym and want to stay strong, resilient, and energised through the darker months, Vitamin D is one supplement you shouldn’t skip.

It’s cheap, effective, and essential for your immune system, muscle function, and mood. In short: a small daily habit that keeps your body performing at its best all winter long.

Want to improve your health and fitness? Let the AdMac Fitness Personal Trainers help…

AdMac Fitness has been helping the people of East London transform their health and fitness for nearly a decade.

We help people using tried and tested fitness approaches. Our expert team of personal trainers, based in both Bow and South Woodford can help you get a grip of your health forever. With our guidance and experience, you can relax knowing that your fitness journey is going to be guided by some of the best personal trainers in East London.

For more information on who we are, what we do and how we can help you achieve your health and fitness goals, contact us on… 07921465108 or email us at admacfitness@gmail.com. We look forward to hearing from you!

Our locations are…

AdMac Fitness: Arch 457 Robeson St, London E3 4JA

AdMac Fitness South Woodford: Unit 4 Marlborough Business Centre, 96 George Lane, South Woodford, London, E18 1AD