We often think of vitamin D as the bone health vitamin—and yes, it does play a key role in helping your body absorb calcium and keep bones strong. But that’s just the tip of the iceberg.
What if I told you that your ongoing fatigue, mood dips, blood sugar spikes, or even gut issues might be linked to low levels of vitamin D?
In my nutritional therapy practice, I work with many clients who have no idea their vitamin D levels are less than optimal. And when we finally test? It all starts to make sense.
What Does Vitamin D Actually Do (Besides Support Bones)?
Vitamin D is a fat-soluble vitamin that behaves more like a hormone in the body. It plays a much bigger role in your overall wellbeing than many people realise. Here’s what it supports:
- Immune system regulation – Helps your immune system respond effectively without overreacting (think: fewer bugs, less inflammation).
- Gut barrier integrity – Supports tight junctions between cells in your gut, keeping that gut lining healthy.
- Microbiome health – Encourages the colonisation of beneficial gut bacteria.
- Insulin regulation – Aids insulin secretion and can improve insulin sensitivity, helping to regulate blood sugar.
- Calcium absorption – Helps your body absorb calcium from food in the gut.
- Mood and brain health – Emerging evidence suggests links between low vitamin D and symptoms like depression, low mood, and brain fog.
How Vitamin D Works with Other Nutrients
Vitamin D doesn’t work in isolation. To be activated and used effectively by the body, it needs:
- Fats – As a fat-soluble vitamin, vitamin D requires dietary fats for proper absorption.
- Magnesium – Needed to convert vitamin D into its active form. Think green leafy veg, chickpeas, lentils, beans, nuts, and seeds.
- Vitamin K2 – Works alongside vitamin D to direct calcium to the bones (where it belongs) and away from soft tissues like arteries. K2 is produced by your gut bacteria when you eat leafy greens rich in vitamin K1.
So if you’re supplementing with vitamin D but missing these co-factors, you might not be reaping the full benefits.
Signs of Vitamin D Deficiency
Some of the most common symptoms of low vitamin D levels include:
- Feeling constantly tired or low in energy
- Low mood or irritability
- Frequent infections or slow recovery from illness
- Muscle weakness or joint aches
- Poor concentration or brain fog
- Hormonal imbalances
- Gut issues and inflammation
Sound familiar? You’re not alone. In fact, most people in the UK don’t get enough vitamin D—especially through the winter months.
Why Getting Enough Vitamin D in the UK Is So Tricky
The best source of vitamin D is sunlight, but in the UK (particularly in Scotland), sunshine can be in short supply. To make vitamin D through your skin, the UV index needs to be high enough—something that typically only happens between April and September when your shadow is shorter than you are.
Sun creams, indoor lifestyles, and even clothing can reduce vitamin D synthesis.
Plus, some people are at higher risk of vitamin D deficiency, including:
- People with darker skin (melanin reduces the skin’s ability to produce vitamin D)
- Those with diagnosed gut conditions like coeliac disease or IBD (which affect nutrient absorption)
- People following low-fat diets (which impair vitamin D absorption)
- Individuals with SNPs (single nucleotide polymorphisms) on the vitamin D receptor gene
What About Vitamin D in Food?
You can get vitamin D from food, but not in the quantities your body really needs. Good sources include:
- Oily fish (like salmon, mackerel, sardines)
- Egg yolks
- Fortified dairy products or plant milks
- Sunlight-activated mushrooms (great for vegans)
Still, for most people, diet alone won’t provide enough—especially during the darker half of the year.
Government Guidelines on Supplementing
The UK Government recommends that everyone take a vitamin D supplement between October and March to prevent deficiency. The safe upper limit is 4000 IU per day unless prescribed otherwise.
And while vitamin D supplementation is generally safe, more is not always better. Too much can cause hypercalcaemia (a build-up of calcium in the blood), which may affect the heart and kidneys.
This is why I always recommend: test, don’t guess.
How to Test Your Vitamin D Levels
With the NHS under pressure, most GP practices will only test your vitamin D if there’s a clear clinical reason. But you don’t need to wait for an appointment.
You can now order a simple home finger-prick vitamin D test through an NHS laboratory in England. You do the test at home, pop it in the post, and get your results via email.
In my clinic, I recommend testing your vitamin D levels:
- At the start of autumn (October)
- At the end of winter (March)
That way, we can supplement safely and confidently—ensuring you’re getting enough without overdoing it.
Want to Know What Your Vitamin D Level Is?
Knowing your numbers is one of the most empowering steps you can take when it comes to your health. If you’ve been feeling off—tired, low, foggy—it might not just be “life.” It could be your vitamin D calling out for help.
Speak to me about how to order a test and find out how much vitamin D you need to reach optimal levels.
🔗 Book a FREE call and let’s chat!