Why Is My Vitamin D Still Low Despite Taking Supplements?
You take vitamin D every day. You remember your capsule, follow the instructions and expect your next blood test to show an improvement.
Then the result comes back: your vitamin D is still low.
It can be frustrating—and in a sunny city like Perth, it can seem particularly confusing.
But living somewhere with plenty of sunshine does not automatically mean you will have adequate vitamin D. Time spent indoors, clothing, sun-protection habits, darker skin pigmentation, age, body composition and certain health conditions can all influence vitamin D status.
And if your vitamin D remains low despite taking a supplement, the answer is not always as simple as taking more. The dose, consistency, absorption, your individual response and even the form of vitamin D you are taking can all matter.
One form that deserves more attention is calcifediol, also known as 25-hydroxyvitamin D3.
Why might vitamin D remain low despite supplementation?
If your 25(OH)D level is still low after supplementation, several factors may need to be considered.
1. The dose may not be enough for your individual needs
People respond differently to vitamin D supplementation. Your starting vitamin D level, body size, diet, sun exposure and other factors can influence how much your blood level changes.
A dose that is adequate for one person may not produce the same response in another.
This is one reason vitamin D supplementation is best considered in the context of your individual blood results and circumstances rather than by comparing your dose with someone else's.
2. You may not be taking it consistently
This sounds obvious, but it is one of the first things worth checking.
Missing doses regularly can make an otherwise appropriate supplementation plan less effective.
If you are taking vitamin D as prescribed or recommended but finding it difficult to take consistently, discuss this with your healthcare professional rather than simply increasing the dose.
3. Absorption may be an issue
Vitamin D is fat-soluble, and normal fat digestion and absorption contribute to its uptake.
Conditions affecting the gastrointestinal tract, pancreatic function or bile flow can interfere with absorption of fat-soluble vitamins.
Certain medications and medical conditions can also affect vitamin D metabolism.
If your 25(OH)D remains low despite taking an appropriate supplement consistently, your healthcare professional may consider whether absorption, medication interactions or another underlying factor could be contributing.
4. Body composition can influence your response
Vitamin D is stored in body fat. People with higher amounts of body fat may have lower circulating vitamin D concentrations and may require different supplementation strategies to achieve the same blood concentration.
This is another reason why simply comparing your dose with someone else's is not particularly useful.
5. The form of vitamin D may matter
Most standard vitamin D supplements contain vitamin D3 (cholecalciferol).
Vitamin D3 works well for many people. However, it first needs to be converted in the liver into 25(OH)D, or calcifediol.
Calcifediol is already at this stage of the pathway. Taking calcifediol therefore bypasses the initial hepatic hydroxylation step.
It still undergoes further metabolism before producing the active vitamin D hormones.
This difference in how the two forms are processed is one reason researchers have investigated whether calcifediol can raise blood 25(OH)D more rapidly and predictably than conventional vitamin D3.
Vitamin D3 vs calcifediol: what's the difference?
Vitamin D3 (cholecalciferol)
Vitamin D3 is the form produced naturally in your skin after exposure to UVB radiation. It is also the most common form found in vitamin D supplements.
After absorption, vitamin D3 is transported to the liver, where it is converted into 25(OH)D, or calcifediol.
Calcifediol
Calcifediol is 25-hydroxyvitamin D3—the form produced after the initial liver conversion of vitamin D3.
Taking calcifediol therefore bypasses that initial hepatic hydroxylation step. It still undergoes further metabolism before producing active vitamin D hormones.
Because calcifediol is already closer to the circulating form measured in a standard vitamin D blood test, it can produce a more rapid increase in serum 25(OH)D in some circumstances.
What does this mean in practice?
For many people, vitamin D3 remains an effective and appropriate form of supplementation.
Calcifediol may be worth discussing with a healthcare professional when conventional vitamin D3 supplementation has not produced the desired increase in 25(OH)D, or when a more rapid increase is clinically appropriate.
The choice between vitamin D3 and calcifediol should take into account your blood results, medical history, medications, absorption and the reason supplementation is being used.
It is also important not to change your vitamin D dose or switch formulations simply because one form appears more potent. Calcifediol can produce a more rapid increase in 25(OH)D, so dosing needs to be considered carefully.
Can food help if your vitamin D is low?
Yes, although diet alone may not be enough to correct a significant deficiency.
Good dietary sources of vitamin D include:
Oily fish such as salmon and sardines
Egg yolks
UV-exposed mushrooms
Some fortified milk and dairy alternatives
The amount of vitamin D in food can vary considerably depending on the specific food, serving size, fortification and preparation method.
Food is best viewed as part of an overall strategy rather than a replacement for clinically appropriate supplementation when deficiency has been diagnosed.
A balanced diet also provides protein, calcium, magnesium and other nutrients that support bone and general health.
What are the signs of vitamin D deficiency?
Vitamin D deficiency does not always cause obvious symptoms.
When symptoms do occur, they can include:
Tiredness
Muscle weakness
Muscle or bone discomfort
These symptoms are nonspecific and can occur for many other reasons, so they should not be used to diagnose vitamin D deficiency by themselves.
A blood test is used to assess vitamin D status, and your healthcare professional can interpret the result in the context of your individual circumstances.
Why vitamin D matters
Vitamin D plays an important role in calcium and phosphate regulation and contributes to normal bone mineralisation and muscle function.
Its active metabolites also act through vitamin D receptors in many tissues throughout the body.
However, it is important not to overstate what vitamin D supplementation can do.
Vitamin D is essential, but increasing your blood level above what is clinically appropriate does not automatically provide additional health benefits.
The goal is to correct deficiency and maintain an appropriate level—not simply to achieve the highest possible number.
Summary
Sun-safe habits, a balanced diet and appropriate medical care all contribute to maintaining healthy vitamin D status.
If your vitamin D remains low despite supplementation, don't simply increase the dose yourself. Your healthcare professional can review your blood results, adherence, dose, medications, absorption and individual circumstances to determine the most appropriate approach.
Medical information disclaimer
This article provides general health information and is not a substitute for individual medical advice, diagnosis or treatment. Vitamin D treatment should be tailored to your blood results, medical history and individual circumstances. Speak with your GP or other qualified healthcare professional before starting, stopping or changing vitamin D treatment.
Book an Appointment
Book an appointment with me, a naturopath in Perth, and let's look at your results, supplementation, diet and individual circumstances together and explore what may be standing between you and healthier vitamin D levels.
References
Alonso-Pérez, J. L., et al. (2024). Relationship between serum vitamin D levels and chronic musculoskeletal pain in adults: A systematic review. Nutrients, 16(23), 4061. https://doi.org/10.3390/nu16234061
Amrein, K., Scherkl, M., Hoffmann, M., et al. (2020). Vitamin D deficiency 2.0: an update on the current status worldwide. European Journal of Clinical Nutrition, 74(11), 1498–1513.
Bouillon, R. (2019). Vitamin D and health—the missing vitamin in humans. Pediatrics & Neonatology, 60(3), 237–244.
Charoenngam, N., & Holick, M. F. (2020). Immunologic effects of vitamin D on human health and disease. Nutrients, 12(7), 2097. https://doi.org/10.3390/nu12072097
Giannini, S., et al. (2022). The immunologic profile of vitamin D and its role in different immune-mediated diseases: An expert opinion. Nutrients, 14(3), 473. https://doi.org/10.3390/nu14030473
Graeff-Armas, L. A., Kaur, I., Masi, P., & Heaney, R. P. (2020). Supplemental 25-hydroxycholecalciferol is more effective than cholecalciferol in raising serum 25-hydroxyvitamin D concentrations in older adults. The Journal of Nutrition, 150(1), 73–81.
Holick, M. F. (2007). Vitamin D deficiency. New England Journal of Medicine, 357(3), 266–281.
Quesada-Gomez, J. M., & Bouillon, R. (2018). Is calcifediol better than cholecalciferol for vitamin D supplementation? Osteoporosis International, 29(8), 1697–1711.
Vaes, A. M., Tieland, M., de Regt, M. F., Wittwer, J., van Loon, L. J. C., & de Groot, L. C. P. G. M. (2018). Dose-response effects of supplementation with calcifediol on serum 25-hydroxyvitamin D status and its metabolites: A randomized controlled trial in older adults. Clinical Nutrition, 37(3), 808–814.
Comments