7 Reasons Your Vitamin D Levels Are Too Low

You know when you feel like you’re trying to do everything right then — boom, your doctor says your vitamin D levels are too low?

Well, you’re not alone. Lots of us are deficient in vitamin D. In fact, it is the most widespread nutrient deficiency in the Western world.

But you have to make sure you keep your vitamin D levels up. Vitamin D is critical for calcium absorption and for your immune system to work correctly.

So why are your vitamin D levels so low? And what can you do about it?

Who Tends to Have Low Vitamin D?

  • People who frequently get ill. With low vitamin D levels, your body might not be able to fight off infections like COVID-19.
  • People with thyroid problems. Low vitamin D levels have been linked to autoimmune diseases like Hashimoto’s thyroiditis.
  • People with other autoimmune diseases like rheumatoid arthritis.
  • Some people with depression tend to have low vitamin D.
  • Many athletes are vitamin D deficient leading to reduced muscle function and increased risk of stress fractures, inflammation and illnesses.
  • People over the age of 50 years old.
  • People with darker skin.

Personalise your vitamin D needs and get your personal plant-based health score FOR FREE — click here.

Why Low Vitamin D? 7 Reasons Your Vitamin D Levels Are Too Low

1. Not getting enough sunlight

Your body creates vitamin D from direct sunlight on your skin when outdoors in the warmer months. Vitamin D is made in your skin and stored in fat after exposure to sunlight. Your body releases it when the sunlight is gone.

Try to sunbathe with uncovered forearms and legs (without sunscreen) for at least 15 minutes each day between 10:00 and 15:00 from May to September.

Always remember to cover up or protect your skin if you’re out in the sun for long periods to reduce the risk of skin damage and skin cancer.

2. Using too much suncream

Suncream blocks UV-B rays from entering our skin. That’s good for the most part because it UV-B rays make us burn and can damage our DNA. But we need small doses of UV-B rays to make vitamin D too. So it’s best to make sure you get 15 minutes of sun every day without suncream in the summer.

3. Not supplementing vitamin D

Dietary intake of vitamin D is essential if you have insufficient sunlight exposure, wear a lot of sunscreens or in the winter months. During the autumn and winter, you need to get vitamin D from supplements because the sun isn’t strong enough for the body to make vitamin D. The recommended dose of vitamin D is 10 µg per day (1).

4. Not eating foods high in vitamin D

We mostly make it from sunlight. But because the only main food source of vitamin D is fish those who avoid animal foods may have lower levels.

However, animals make vitamin D from sunlight just like humans. So getting vitamin D from dairy and fish is not necessary as long as you’re getting it elsewhere.
Many plant-based milks and other foods are now fortified with vitamin D. So you can get some vitamin D from fortified foods. But this is an unreliable source as cooking can reduce the levels. Make sure you get your vitamin D from sunlight or supplements instead wherever possible.

5. Following a very low-fat diet

Vitamin D is fat-soluble. In the winter while you can’t make enough vitamin D through sunlight exposure you need to eat enough fat to absorb vitamin D from supplements or food.

6. Being over 50 years old

The efficiency of the synthesis of vitamin D in our skin decreases with age. After the age of 50 vitamin D synthesis starts to decline significantly and you might not be able to make enough from sunlight.

7. Genetics

Some genes affect your absorption and conversion of vitamin D into the active form you need.

a. VDR
The vitamin D receptor (VDR) is the receptor for active vitamin D. The VDR contributes to regulating calcium levels by stimulating calcium absorption from your gut.

Depending on your genes, some people have lower functioning vitamin D receptors. And these people may need higher levels of vitamin D. Common genetic variations of your vitamin D receptors (VDRs) could result in VDRs which don’t bind to vitamin D as well.

b. GC
Vitamin D-binding protein (also called GC) is responsible for carrying the vitamin D synthesized in our skin to our cells where it is needed.

But some people have a genetic variation in GC, which makes transporting vitamin D from your skin much less efficient. If you have this genetic variation, a low-fat diet may increase your risk of depression.

c. DHCR7
Vitamin D from sunlight forms in our skin from the precursor to cholesterol. DHCR7 (7-dehydrocholesterol reductase) converts this precursor into cholesterol, thereby removing the substrate from the pathway of vitamin D3. People with the gene for upregulated cholesterol synthesis may not be able to make enough vitamin D from sunlight alone.

d. CYP2R1
CYP2R1 converts vitamin D from your diet or sunlight into calcifediol (vitamin D2). If you have the gene for slower CYP2R1 conversion, you might need a higher dose of vitamin D.

e. CYP24A1
CYP24A1 regulates your vitamin D levels by getting rid of any excess. It does this by converting active vitamin D to inactive vitamin D. Depending on your genes; this process could be too quick, resulting in too much vitamin D becoming inactive.


No matter which diet you follow it’s important to stay on top of your vitamin D levels. And personalising your vitamin D intake depending on your needs, genes and lifestyle is crucial to make sure you’re getting enough.

Personalise your vitamin D needs and get your personal plant-based health score FOR FREE — click here.


  1. https://www.gov.uk/government/publications/sacn-vitamin-d-and-health-report



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Ellie Busby (MSc, mBANT)

Ellie Busby (MSc, mBANT)


I’m Ellie: scientist, runner, baker,registered nutritionist and genetics geek at Vojo. Follow me for personalised weight loss & plant-based diet tips.