There is no doubt that everyone can benefit from vitamin D intake, either through sunlight, diet, or supplementation. UK health professionals recommend 400IU of Vitamin D supplementation over the winter months and for certain groups, advise year-round supplementation of the vital nutrient. With higher dose supplements are available, is it possible to consume too much vitamin D? Nutritionist Will Jordan takes a deep dive into the research to explore how much you should really take.
What is Vitamin D?
Vitamin D is an essential vitamin for everyone. This fat-soluble vitamin has two main forms, ergocalciferol (vitamin D2) which is sourced from plants and fungi, and cholecalciferol (vitamin D3) which is found in animal sources and made in our skin using sunlight, and some specific lichen. [1] We need vitamin D as it plays several key roles in the body, including influencing bone health, regulating calcium and phosphate levels, modifying immune function, and cell division, specialisation, and programmed death. [2]
The ‘traditional’ way that humans would get vitamin D is through sunlight. When our skin is exposed to UVB rays from the sun, it converts 7-dehydrocholesterol, a molecule derived from cholesterol, into previtamin D3. Over the next few hours, our body heat re-arranges provitamin D3 into the active form vitamin D3, scientifically known as 1,25(OH)2D, which is responsible for many health benefits. [3] Skin colour plays a role in vitamin D production, as darker skin tones are associated with lower vitamin D status. Individuals with darker skin tones have higher melanin in their skin, which reduces UVB penetration into the skin, and thus lowering vitamin D production. [4]
What are the recommendations?
Vitamin D is commonly measured in 2 different units, micrograms (mcg, ug, or μg) and international units (IU). An international unit is a measurement of the biological activity or effect of a substance which are consistent across countries. [5] Each vitamin will have its own IU value, and 5mcg of vitamin D is equal to 200IU. The current recommendations for vitamin D is 400IU equating to 10 micrograms (mcg) per day year-round in children from one years old through to adulthood. This recommendation does not include sunlight exposure as this depends on individual behaviour, such as how much time you spend outside, and where you are in the UK. [6] The NHS advises everyone to consider taking a supplement containing 400IU during the autumn and winter months. Vitamin D3 is a fat-soluble vitamin, and it is predominantly stored in adipose tissue (fat) which can be released slowly over time. Much smaller amounts of vitamin D is stored in the liver and muscle tissues. This is how ancient humans survived the winter months at higher latitudes, and why we don’t need to take high doses of vitamin D year-round. [7]
What does the science say, how much vitamin D is actually recommended?
The recommended dose is 400IU per day, which is for most people a good maintenance dose for healthy individuals with lighter skin tones over the winter months, and those darker skin tones should consider supplementing 400IU per day year-round in the UK. However, there is a diversity of opinions that exist from governments and scientific societies which suggest supplementing anywhere between 400-1,000IU per day in healthy adults. [8] There is research that suggests that those living with obesity may need slightly higher doses ranging between 1,600-2,000IU per day to reach optimal vitamin D levels in the body. [9]
A clinical trial has shown individuals who supplemented with Viridian Nutrition’s Vitamin D3 improved their levels of the micronutrient - avoiding vitamin D deficiency during the winter months. Two parallel randomised controlled trials were undertaken in England and Brazil, where women were supplemented with 600IU of vitamin D per day throughout the winter months. Both groups found improved vitamin D levels significantly regardless of latitude. Listen to our head director discuss the study here [10]
Why can GPs give much higher doses?
In specific situations, extremely high doses of vitamin D3, 10,000IU (250mcg) or higher can be prescribed by GPs under medical supervision. In extreme deficiency, a loading dose of vitamin D can be given. This is a high strength course of vitamin D treatment that is usually taken over a short time to lift vitamin D levels quickly. In short term use, normally for a few weeks, this is safe and can effectively raise vitamin D levels to an adequate amount. [11] Following this, a maintenance dose of vitamin D to prevent deficiency may be recommended and this can range from 400-2,000IU per day. [12]
What happens if you take too much?
Extreme doses of Vitamin D3 from supplements over long periods of time can cause liver levels of vitamin D to rise. This causes more calcium to be absorbed from the gut and released from the bone. This elevates blood calcium levels and causes hypercalcemia. [13] A double-blind, randomised, control trial (RCT) included 311 participants aged 55 to 70 years old who were split into 3 equal groups were supplemented either 400IU, 4,000IU or 10,000IU daily for 3 years. The results from this study found that radial bone mineral density in the 4,000IU and 10,000IU groups compared to 400IU group was significantly lower at the end of the trial compared to the start. Only the 10,000IU found a reduction in the bone mineral density of the tibia bone compared to the 400IU group. Bone strength was not affected, however, researchers concluded that extremely high doses of vitamin D daily was not beneficial for bone health. Additionally, 10 per cent of the 10,000IU group suffered from hypercalcaemia by the end of the study, as well as 3 per cent of the 4,000IU group. [14]
The mechanism for this is vitamin D increases calcium mobilisation from the bone into the blood, reducing bone mineral density, as well as more calcium absorption from foods. Excess vitamin D causes too much calcium in the blood and can lead to hypercalcemia. This is known as vitamin D intoxication. Hypercalcemia is rare, but thresholds are also unknown as symptoms are influenced by dose, duration and individual calcium metabolism and underlying issues. Whilst rare, it is commonly linked to prolonged high-dose supplementation and mismanagement. [15] [16] [17] Because of this, an Tolerable Upper Intake Level was established to be 4,000IU per day by the European Food Safety Authority (EFSA), 10 times the recommended amount vitamin D recommended by UK Health Professionals. [18]
Conclusion
In conclusion, there is no perfect amount of vitamin D, but supplementing anywhere between 400 -2,000IU per day from food supplements is known to be safe and improve vitamin D levels. Everyone is unique and needs will vary based on numerous factors from location, age and life stage. It is important to get vitamin D levels tested before and during supplementing higher doses in excess of 2,000IU to ensure you are not raising’ levels too high.
When choosing quality supplements opt for those which contain therapeutic does and researched ingredients. Always read the label and avoiding supplements containing artificial additives, binders and fillers or other manufacturing aids. Instead look for formulations which benefit the body nutritionally.
Author: Will Jordan, BSc (Hons) MSc, is a Nutrition Advisor at Viridian Nutrition. He holds a Master’s degree in Sports and Exercise Nutrition, BSc in Food and Nutrition.
References:
[1] European Food Safety Authority (EFSA). Scientific Opinion on Dietary Reference Values for vitamin D. EFSA Journal. 2016; 14 (10) e04547
[2] Basit S. Vitamin D in health and disease: a literature review. British Journal of Biomedical Science. 2013; 70 (4) 161-172
[3] Whiting SJ, Calvo MS, & Vatanparast H. Chapter 43 – Current Understanding of Vitamin D Metabolism, Nutritional Status, and Role in Disease Prevention. Nutrition in the Prevention and Treatment of Disease (4th edition). 2017; 937-967
[4] Young AR, Morgan KA, Ho TW, Ojimba N, Harrison GI, Lawrence KP, Jakharia-Shah N, Wulf HC, Cruisckshank JK, & Philipsen PA. Melanin has a Small Inhibitory Effect on Cutaneous Vitamin D Synthesis: A Comparison of Extreme Phenotypes. The Journal of Investigative Dermatology. 2020; 140 (7) 1418-1426
[5] Hansen YBL. Recommendations on Measurement Units – Why and How. The Journal of the International Federation of Clinical Chemistry and Laboratory Medicine. 2019; 30 (3) 250-275
[6] Public Health England. The Scientific Advisory Committee on Nutrition (SACN) recommendations on vitamin D. SACN vitamin D and health report. 2023. Available online https://www.gov.uk/government/publications/sacn-vitamin-d-and-health-report?utm_source=chatgpt.com [26/01/2026]
[7] Park CY, & Han SN. The Role of Vitamin D in Adipose Tissue Biology: Adipocyte Differentiation, Energy Metabolism, and Inflammation. Journal of Lipid and Atherosclerosis. 2021; 10 (2) 130-144
[8] Ramasamy I. Vitamin D Metabolism and Guidelines for Vitamin D Supplementation. The Clinical Biochemist Reviews. 2020; 41 (3) 103-126
[9] Bassatne A, Chakhtoura M, Saad R, & Fuleihan GEH. Vitamin D supplementation in obesity and during weight loss: A review of randomises controlled trials. 2019; 92, 193-205
[10] Mendes MM. Interaction between vitamin D supplementation and sunlight exposure in women living in opposite latitudes (the D-SOL study). University of Surrey. 2020. Available online https://openresearch.surrey.ac.uk/esploro/outputs/doctoral/99514624102346 [06/02/2026]
[11] Hosseini B, Tremblay CL, Longo C, Glochi S, White JH, Quach C, Ste-Marie LG, Platt RW, & Ducharme FM. Oral vitamin D supplemental therapy to attain a desired serum 25-hydroxyvitamin D concentration in essential healthcare teams. Trials. 2022; 23, 1019
[12] Pludowski P, Takacs I, Boyanov M, Belaya Z, Diaconu CC, Mokhort T, Zherdova N, Rasa I, Payer J, & Pliz S. Clinical Practive in the Prevention, Diagnosis and Treatment of Vitamin D Deficiency: A Central and Eastern European Expert Consensus Statement. Nutrients. 2022; 14 (7) 1483
13] Morita R, Yamamoto I, Takada M, Ohnaka Y, & Yuu I. Hypervitaminosis D. Nihon Rinsho. 1993; 51 (4) 984-988
[14] Burt LA, Billington EO, Rose MS, Raymond DA, Hanley DA, & Boyd SK. Effect of High-Dose Vitamin D Supplementation on Volumetric Bone Density and Bone Strength. JAMA. 2019; 322 (8) 736-745
[15] National Institute of Diabetes and Digestive and Kidney Diseases. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury [Internet]. National Library of Medicine (US). 2012. Available from: https://www.ncbi.nlm.nih.gov/books/NBK547852/ [27/01/2026]
[16] Lee JP, Tansey M, Jetton JG, & Krasowski MD. Vitamin D Toxicity: A 16-Year Retrospective Study at an Academic Medical Centre. Laboratory Medicine. 2018; 49 (2) 123-129
[17] Alkundi A, Momoh R, Musa A, & Nwafor N. Vitamin D intoxication and severe hypercalcaemia complicating nutritional supplements misuse. British Medical Journal Case Reports. 2022; 15, e250553
[18] EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific Opinion on the Tolerable Upper Intake of vitamin D. EFSA Journal. 2012; 10 (7) 2813
The information contained in this article is not intended to treat, diagnose or replace the advice of a health practitioner. Please consult a qualified health practitioner if you have a pre-existing health condition or are currently taking medication. Food supplements should not be used as a substitute for a varied and balanced diet.
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