If you’ve been feeling tired, run down, or just a bit “off”, your vitamin D levels might be worth checking.
Vitamin D plays an essential role in supporting normal immune function, muscle function, and bone health.¹ Yet despite its importance, vitamin D deficiency is one of the most common nutrient deficiencies worldwide.
Research suggests:
• Around 1 billion people are deficient
• Around 50% of the global population have insufficient levels²
The challenge?
Low vitamin D often develops slowly and symptoms can be subtle or overlap with other issues.
8 Signs of Low Vitamin D
1. You Keep Getting Ill
Vitamin D supports the normal function of your immune system.¹ Research suggests people with lower vitamin D levels may experience more frequent respiratory infections like pneumonia, bronchitis.³ The lack of sunlight in the winter may well help to explain why we’re all more prone to illness in the darker winter months.
2. Cuts and Injuries Are Slow to Heal
Your body needs vitamin D to help manage inflammation in response to injury.⁴ If you've noticed that small cuts or bruises seem to hang around longer than they should, low vitamin D could be playing a part.
3. Aches in Your Back or Bones
Vitamin D helps your body absorb calcium - the mineral that keeps your bones strong.¹ Without enough of it, you might notice a dull ache in your lower back or joints.⁵
4. Weak Bones
This one is especially important as you get older. Without enough vitamin D, your body can't use calcium properly. Over time, this can weaken your bones and make fractures more likely.⁶
5. Feeling Tired All the Time
There are a hundred reasons you might feel tired - poor sleep, stress, a busy schedule. But persistent, unexplained fatigue is one of the most commonly reported symptoms of low vitamin D.⁷ Low vitamin D status has also been linked to poorer sleep quality in some populations, which may contribute to fatigue symptoms.¹⁰
6. Hair Loss
Vitamin D is involved in the regulation of hair follicle growth and cycling. Low levels have been associated with alopecia areata - an autoimmune condition where the body attacks hair follicles, causing small patches of hair loss.⁸ While vitamin D plays a role in immune function, it’s not a standalone solution, and hair loss can have multiple underlying causes.
7. Low Mood or Feeling Flat
Low mood or feeling flat can be more common in the winter months when sunlight is sparse. Some studies have found associations between low vitamin D levels and mood changes.⁹ Vitamin D should not be considered a treatment for mood disorders, but it may play a role in supporting healthy psychological function.
8. Poor sleep quality
If you're sleeping enough hours but still waking up feeling unrested, vitamin D could be a factor. A meta-analysis of multiple studies found that people with low vitamin D levels were significantly more likely to experience poor sleep quality and shorter sleep duration.¹⁰ The exact mechanism isn't fully understood, but the association has shown up consistently across different studies.
Why Is Vitamin D Deficiency So Common?
Here's the thing most people don't realise: your body makes vitamin D when sunlight hits your skin. You don't get much from food. So if you're not getting regular sun exposure, your levels can drop.
You're more likely to be low in vitamin D if you:
• Live somewhere with limited sunshine (the UK, northern Europe, etc.)
• Spend most of the day indoors - whether that's an office, a warehouse, or at home
• Work nightshifts.
• Are over 50 - your skin produces less vitamin D as you age
• Have darker skin, which needs more sun exposure to make the same amount
• Have a digestive condition that affects how well you absorb nutrients
Very few foods naturally contain vitamin D, which makes it harder to maintain levels through diet alone.
How Do You Know If You're Deficient?
The honest answer: you can't tell from symptoms alone. All of the signs above can be caused by other things too. The only reliable way to check is with a simple blood test. Your GP can arrange this, or you can order a home test kit. If your levels come back low, your doctor will usually recommend a higher-dose supplement for a few weeks to bring things back up.
How to Maintain Healthy Vitamin D Levels
It usually comes down to three things:
1. Get some sun.
Around 10–30 minutes of midday sunlight on bare skin, a few times a week, is a good starting point - depending on where you live and your skin type. In the UK between October and March, the sun isn't strong enough to make a difference.
2. Eat vitamin D-rich foods.
Oily fish, egg yolks, and fortified foods are the main dietary sources. If you're plant-based, fortified plant milks and UV-exposed mushrooms can help - but food alone is rarely enough.
3. Take a D3 supplement.
Public Health England recommends everyone think about taking a daily vitamin D supplement during autumn and winter. If you don't get much sun year-round, daily supplementation may be worth considering all year.
A Simple Way to Support Your Vitamin D Intake
If you're looking for an easy way to stay on top of your daily intake, Vivo Life's Vegan Liquid D3 keeps things straightforward:
• 2,000 IU of vitamin D3 per serving - a widely recommended daily amount
• Made from algae, not sheep's wool - so it's fully vegan
• Includes vitamin K2, which supports the maintenance of normal bones¹
• Comes in an oil-based liquid - and since vitamin D is fat-soluble, having fat built into the supplement helps your body absorb it properly
A few drops a day. Particularly useful during the colder, darker months when sunshine alone isn't going to cut it.
Does It Matter Whether You Take Capsules or Liquid?
Vitamin D is what's called a fat-soluble vitamin. In simple terms, your body absorbs it better when there's some fat present.¹ A lot of vitamin D supplements come as dry tablets or capsules. A liquid supplement that's already dissolved in oil provides that fat alongside the vitamin D, which may help support absorption - especially if you're taking it between meals
Common Questions About Vitamin D Deficiency
How long does it take to fix a vitamin D deficiency?
It depends on how low your levels are and what dose you take. Most people start to feel a difference within a few weeks, but it can take 2–3 months of consistent supplementation to bring levels back into a healthy range. Your doctor can advise on the right dose for you.
Can you get enough vitamin D from food alone?
For most people, no. Very few foods naturally contain enough vitamin D to meet your daily needs. Oily fish and fortified foods help, but sunlight and supplementation are usually needed — especially during winter.²
How much vitamin D should I take per day?
In the UK, the NHS recommends 400 IU (10 micrograms) per day as a minimum for adults. Many healthcare professionals suggest between 1,000 and 2,000 IU for people who are at higher risk of deficiency. If you're unsure, check with your GP.¹¹