Vitamin D in Winter: Why Your Levels Matter More Than Ever

With the shortest day of the year only a few weeks away, most of us are now leaving home in the dark and coming back in the dark. It’s one of the most dramatic seasonal shifts your body goes through, and it’s completely normal to feel your energy dip or your resilience change at this time of year.

Many people assume winter illnesses are simply caused by “more germs going around,” but research and public health guidance show that the condition of the host matters just as much as the environment.
This idea — sometimes called terrain theory — suggests that how well you adapt, recover and stay resilient depends heavily on what’s happening inside your body.

And one of the biggest winter factors influencing your internal “terrain” is vitamin D.

Vitamin D: Why It Drops in Winter

Vitamin D is often called the sunshine vitamin because your skin produces it when exposed to UVB light.
But between October and March, UVB levels in the UK and Ireland are too low for most people to make enough vitamin D — even on bright days.

This is why additional vitamin D supplementation is recommended through autumn and winter, as sunlight simply isn’t strong enough to maintain normal levels.

Harvard’s School of Public Health also explains that vitamin D supports immune cell communication and balanced immune responses — something particularly important during the colder months: Read it here

So if you notice changes in your mood, energy or general resilience in December, there’s a biological reason behind it.

How the Nervous System and Immune System Work Together

While nutrition lays a foundation, your immune system doesn’t operate alone.
The nervous system plays a major role in coordinating immune activity — something the Cleveland Clinic describes as a complex communication network running throughout the body: Cleveland Clinic Source

Your spine protects the spinal cord, which is the main communication pathway between the brain and the rest of the body. When spinal segments become stiff or restricted, it can add stress to the nervous system and affect how efficiently the body adapts to everyday challenges.

Chiropractic adjustments aim to restore healthy spinal mobility so the nervous system can function as clearly and effectively as possible. While chiropractic doesn’t treat illness, many people find they feel more balanced, more adaptable and more resilient when their spine is moving well — especially during the darker winter weeks.

Building a Stronger Terrain as We Approach Christmas

A few weeks before Christmas is an ideal time to provide additional support to your body ahead of the busiest, most demanding part of winter.

Here are some evidence-informed steps that help strengthen your internal terrain:

1. Optimise Your Vitamin D

• Public health organisations recommend supplementation from October to March.

• Include foods such as oily fish, fortified products, and eggs.

• Daylight exposure still benefits your mood and circadian rhythm.

2. Choose Nourishing Winter Foods

Seasonal vegetables, warming soups, lean protein, and ingredients like garlic, ginger and mushrooms help support general wellbeing during colder months.

3. Prioritise Rest

Shorter days naturally shift your body toward rest.
Good-quality sleep helps regulate mood, support recovery and maintain energy.

4. Keep Your Body Moving

Movement improves circulation, supports lymphatic flow and helps counteract winter stiffness. Even 10 minutes of stretching or a brisk walk during daylight can make a noticeable difference.

5. Chiropractic Support for Seasonal Stress

By supporting spinal mobility and clearer nervous system communication, chiropractic care can play a positive role in helping your body adapt to seasonal demands.

Winter Wellbeing: More Than Just Fighting Bugs

It’s easy to focus only on avoiding germs — but winter health is much more about strengthening the terrain within your body.

The UK Health Security Agency offers additional winter wellbeing guidance here: Read more and research shows that repetitive tasks or fatigue — common during the long hours of Christmas cooking or preparing for the holidays — can increase strain in the body. A relevant PubMed study on neuromuscular fatigue can be found here: Pubmed

By supporting your vitamin D levels, caring for your spine and nervous system, and building simple daily habits, you give your body the best chance to stay balanced through the darkest, busiest part of the year.

At Avalon Chiropractic Belfast, we’re here to help you stay mobile, resilient and well supported this winter.
If you’d like guidance or a seasonal check-in, we’re here for you.