Should you be taking vitamin D?

Have you started your vitamin D supplement yet? In the UK, around 1 in 6 adults and nearly 1 in 5 children have levels that fall below recommended guidelines.¹ Deficiency has been on the rise, and health authorities now advise that everyone takes a daily supplement between October and April.

Why? Your main source of vitamin D is sunlight on bare skin. During darker months, there simply isn’t enough sunshine. Add in modern habits like working indoors, driving instead of walking, covering up, or using sunscreen, and it’s easy to see why deficiency risk soars.

So what’s the big deal about vitamin D? It’s not just “another vitamin”. Research shows it plays a role in immune defences, bone strength, inflammation control, mood, and even muscle function.² Here’s how…

1. Immune health

The immune system can be divided into 2 vital parts –

The innate immune response (the “first responders”): This is your body’s immediate, non-specific defence. Think of it as the alarm system that activates the moment something harmful enters your body. It includes barriers like skin, as well as internal reactions such as fever, inflammation, and the release of antimicrobial compounds. Special white blood cells called phagocytes rush in to engulf and destroy pathogens. Vitamin D helps regulate these processes, ensuring your innate immune system responds quickly and effectively without becoming overactive.
The adaptive immune response (the “specialist team”): This arm of the immune system is slower to respond, but far more precise. It involves lymphocytes (B cells and T cells) that learn to recognise and remember specific pathogens. This is how vaccines work – they “teach” your adaptive immune system what to look out for. Vitamin D supports the development and activity of these cells, helping your body produce targeted antibodies and immunological memory so you fight infections faster next time.

Without enough vitamin D, both systems can become less efficient, leaving you more vulnerable to frequent infections or slower recovery. A large 2017 study published in the British Medical Journal found vitamin D to be effective for preventing colds and flu³, so it’s worth having your levels checked this autumn!

For extra support in strengthening your immune system, try our immune-boosting smoothie recipes!

2. Bone health

One of the many roles of vitamin D is to support bone health.⁴ Vitamin D helps your body absorb calcium from food and recycle it through the kidneys. This is essential for strong bones, teeth, and skeletal development. Without it, calcium is wasted, leaving bones more vulnerable.

Check out our article Unleash your inner strength: 8 reasons you should be strength training for more tips on improving your bone health!

3. Inflammation

Low vitamin D is linked to higher levels of C-reactive protein (CRP), a marker of chronic low-grade inflammation. Inflammation is a key factor in conditions like arthritis, heart disease, type 2 diabetes, obesity, dementia, and autoimmune disorders. Correcting low vitamin D may help keep inflammation in check.⁵

4. Mood and mental health

The days are getting darker, but your mood doesn’t have to! As daylight fades, low vitamin D has also been associated with depression, anxiety, and fatigue. Recent research suggests supplementation may ease depressive symptoms, even in people with mild or moderate mood concerns.⁶⁷ It has also been linked to less severe fibromyalgia symptoms.⁸

Who’s most at risk?

Some groups are more vulnerable to deficiency, including:

Pregnant women, breastfed babies and all children under the age of 5*.
Elderly adults – the body’s ability to make vitamin D halves between ages 20–80.
Limited time outside – housebound, hospitalised or living in a care home.
Obesity & underweight – both can increase deficiency risk.
People with darker skin tones naturally have more melanin, which reduces the skin’s ability to make vitamin D. This means they may need significantly longer sun exposure to produce the same amount as people with lighter skin.
Liberal use of sunscreen or extensive skin covering – such as for religious or other reasons.
Genetic factors – common genetic changes are known to affect deficiency risk.
Where you live / time of year – risk increases the further away from the equator you live, especially in winter.

Current UK guidelines on vitamin D

According to the NHS, here’s what you need to know:

Adults and children aged 1+ (including pregnant and breastfeeding women) should aim for 10 micrograms (400 IU) of vitamin D a day.
Babies under 1 year need 8.5-10 micrograms daily, unless they’re drinking 500 ml or more of fortified formula milk (which already contains vitamin D).
From late March/early April to the end of September, most people can make enough vitamin D from sunlight on bare skin, so a supplement isn’t always necessary.
From October to March, everyone is advised to take a daily supplement, because the UK sun isn’t strong enough for vitamin D production in winter.
Certain groups, such as people who spend little time outdoors, cover up, or have darker skin, may still need to supplement year-round.

If you’re already deficient, you may need more to restore healthy levels – this is something your GP can check with a simple blood test.

Test, don’t guess!

A maintenance supplement is sensible for most people, but the best way to know your needs is by testing. Vitamin D levels can be checked through your GP or a home finger-prick kit. Ideally, test twice a year (at the end of summer and the end of winter) to see how your levels shift.

Choosing a vitamin D supplement

When buying vitamin D, look for vitamin D3 (cholecalciferol), which is the most effective form at raising blood levels. Vegan-friendly options are available, usually sourced from lichen. Many standard tablets and sprays provide the recommended 10 micrograms (400 IU) daily dose. If your GP has identified a deficiency, you may need a higher-strength supplement for a period of time – but stick to professional guidance, as too much vitamin D can be harmful.

Some supplements combine vitamin D3 with vitamin K2. K2 helps direct calcium into bones and teeth, and away from soft tissues such as arteries. This means a D3 + K2 formula may be particularly helpful for bone and heart health if you’re taking higher-dose vitamin D over a longer period.

To learn about how the weather can also affect your mood, check out our article Can the weather REALLY affect your mood?.

Any questions? Contact one of our Nutritional Therapists via live chat, weekdays from 8 am to 8 pm.

Should you be taking vitamin D?

1. Immune health

2. Bone health

3. Inflammation

4. Mood and mental health

Who’s most at risk?

Current UK guidelines on vitamin D

Test, don’t guess!

Choosing a vitamin D supplement

References

Questions? Talk to a Nutritional Therapist on live chat!

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