You have been diagnosed with vitamin D deficiency (VDD) and are asking yourself, “Why is my vitamin D low? What am I doing wrong?”
You are not alone.
A whopping 1 billion people worldwide are VDD. 13
I will run through some of the main reasons. Some you can change or improve on. You will have no control over others.
Understanding your vitamin D reading
How low is your vitamin D?
Below are the levels that we work on. Blood tests measure the form 25(OH)D (D3). It is the highest circulating form of vitamin D. 12
| nmol/L | ng/mL | BONE & HEALTH STATUS |
|---|---|---|
| 30 | 12 | Deficient |
| 30 to 50 | 12 to 20 | Insufficient |
| ≥ 50 | ≥ 20 | Adequate |
| > 125 | > 50 | Potential toxicity |
Why is my vitamin D low?
1. You are not getting enough sunshine
This is the ultimate vitamin D source via UVB on the skin.
The skin meets about 90% of the body’s vitamin D needs under normal circumstances. 1
Studies report that in the USA, 41.6% 5 and in Europe, 40% of the population are Vitamin D deficient. 4
Even though midday is the prime production time, avoid the four hours when the sun is highest. This is also the worst time for UV skin damage. Find a balance.
You cover up outdoors
Even in South Africa, almost every third patient is VDD.
Clothing is the main reason for decreased vitamin D production in good sunlight. 6
You need about 40% surface exposure to generate maximum vitamin D levels.
Most of us cover up in the sun because of the risk of skin cancer and aging: long sleeves, hats, and UV-protective buffs.
Sunscreen is not completely to blame
Most online information reports that sunscreen is a cause of VDD.
In my research, I have found that it doesn’t.
One study on whether sunscreen reduces vitamin D production showed low risk. 3 Another agrees that optimal use of sunscreen does not decrease production in healthy individuals. 8
Sunblock is essential these days. It lowers production to some degree, but not substantially.
You might have extended winters
There is less UVB in winter. Thirty minutes in the same spot during summer will produce more vitamin D than in winter. This does not mean that you can go into the sun unprotected. Winter UV rays can still damage and age your skin.
Vitamin D production is also lower in colder climates. People tend to layer up to stay warm and spend less time outdoors.
You live in a high-latitude country
Latitude influences how much UVB gets to Earth. This affects vitamin D production. 4 Reykjavik in Iceland is at a high latitude and gets far less UVB throughout the year than Nicosia in Cyprus. 16
Only some people are lucky enough to live in sunny South Africa.
2. You have a darker complexion
There is some controversy about this. Most studies conclude that darker skin produces less vitamin D. 10,11
There is no guide as to how much extra sunshine is needed. Fan Xiang and associates conclude that the quantity of sun exposure needed for dark-skinned, compared with light-skinned people, to achieve vitamin D sufficiency remains uncertain. 11
3. You are getting older
Kidney function declines slowly with age. The kidney is a critical organ in producing active vitamin D, which decreases by 50% over time.
The precursor of vitamin D3 in the skin decreases by 50% from 20 years old to 80 years of age. 1 A study tried to quantify this. Two age groups (20 to 37 years old and 51 to 69 years old) were exposed to the same 30 minutes of sun and readings taken. Vitamin D3 production can decrease by 13% per decade. The amount produced in the older group was still significant. 7
4. Your body has increased demand
Pregnancy is an example of increased vitamin D demand. It is crucial to diagnose VDD in pregnancy as it causes serious complications for the baby. Some of these are low birth weight, type 1 diabetes, asthma, poor growth after birth, and weak bones. 14,15
5. You are not eating vitamin D-rich foods
Diet is not an easy way to get adequate vitamin D. Very few foods contain significant levels and are mainly fish-based.
Read more about vitamin D-containing foods in another article.
6. You are not absorbing vitamin D
This is rare. It could occur in cystic fibrosis, chronic pancreatic disease, short bowel syndrome, and gastric bypass surgery. 4
7. Your medication is decreasing vitamin D
I’ve included the drug interaction list most likely seen in GP practice. 9 Ask your doctor about your medication.
Laxatives and orlistat, a weight loss drug, prevent vitamin D absorption.
Chronic medication can lower vitamin D levels
| DRUG CLASS | NAME |
|---|---|
| Epilepsy medication | Carbamazepine |
| Chemotherapy tablets | Tamoxifen |
| Anitibiotic | Rifampicin |
| Antifungal | Clotrimazole |
| ARV | Ritononavir, Saquinavir |
| Steroid/cortisone | Dexamethasone |
| High blood pressure medication | Nifedipine, Spironolactone |
| Acne/hirsutism medication | Cyproterone acetate |
| Herbal antidepressant | St. John’s wort |
8. You are overweight
VDD is often seen in patients with a BMI > 30. Obesity is often listed as a sign of vitamin D, but it is a what-came-first situation.
Vitamin D is fat-soluble and is stored in the body’s fatty tissue. The theory is that in overweight people, the vitamin D is stored and not accessed. This leaves blood levels low.
References
- Bocheva, G., Slominski, R. M., & Slominski, A. T. (2021). The Impact of Vitamin D on Skin Aging. International Journal of Molecular Sciences, 22(16). https://doi.org/10.3390/ijms22169097
- Srivastava S. B. (2021). Vitamin D: Do We Need More Than Sunshine?. American journal of lifestyle medicine, 15(4), 397–401. https://doi.org/10.1177/15598276211005689
- Neale, R. E., Khan, S. R., Lucas, R. M., Waterhouse, M., Whiteman, D. C., & Olsen, C. M. (2019). The effect of sunscreen on vitamin D: a review. The British journal of dermatology, 181(5), 907–915. https://doi.org/10.1111/bjd.17980
- Akpınar, Ş., & Karadağ, M. G. (2022). Is Vitamin D Important in Anxiety or Depression? What Is the Truth? Current Nutrition Reports, 11(4), 675-681. https://doi.org/10.1007/s13668-022-00441-0
- Forrest, K. Y., & Stuhldreher, W. L. (2011). Prevalence and correlates of vitamin D deficiency in US adults. Nutrition research (New York, N.Y.), 31(1), 48–54. https://doi.org/10.1016/j.nutres.2010.12.001
- Shipton, E. A., & Shipton, E. E. (2015). Vitamin D and Pain: Vitamin D and Its Role in the Aetiology and Maintenance of Chronic Pain States and Associated Comorbidities. Pain Research and Treatment, 2015. https://doi.org/10.1155/2015/904967
- Chalcraft, J. R., Cardinal, L. M., Wechsler, P. J., Hollis, B. W., Gerow, K. G., Alexander, B. M., Keith, J. F., & Larson-Meyer, D. E. (2020). Vitamin D Synthesis Following a Single Bout of Sun Exposure in Older and Younger Men and Women. Nutrients, 12(8), 2237. https://doi.org/10.3390/nu12082237
- Passeron, T., Bouillon, R., Callender, V., Cestari, T., Diepgen, T. L., Green, A. C., Bernard, B. A., Ly, F., Bernerd, F., Marrot, L., Nielsen, M., Verschoore, M., Jablonski, N. G., & Young, A. R. (2019). Sunscreen photoprotection and vitamin D status. The British Journal of Dermatology, 181(5), 916-931. https://doi.org/10.1111/bjd.17992
- Gröber, U., & Kisters, K. (2012). Influence of drugs on vitamin D and calcium metabolism. Dermato-Endocrinology, 4(2), 158-166. https://doi.org/10.4161/derm.20731
- Libon, F., Cavalier, E., & Nikkels, A. F. (2013). Skin color is relevant to vitamin D synthesis. Dermatology (Basel, Switzerland), 227(3), 250–254. https://doi.org/10.1159/000354750
- Xiang, F., Lucas, R., de Gruijl, F., & Norval, M. (2015). A systematic review of the influence of skin pigmentation on changes in the concentrations of vitamin D and 25-hydroxyvitamin D in plasma/serum following experimental UV irradiation. Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 14(12), 2138–2146. https://doi.org/10.1039/c5pp00168d
- U.S. Department of Health and Human Services. (2023, September 18). Office of dietary supplements – vitamin D. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
- Mistretta, V. I., Delanaye, P., Chapelle, J. P., Souberbielle, J. C., & Cavalier, E. (2008). Vitamine D2 ou vitamine D3? [Vitamin D2 or vitamin D3?]. La Revue de medecine interne, 29(10), 815–820. https://doi.org/10.1016/j.revmed.2008.03.003
- Mulligan, M. L., Felton, S. K., Riek, A. E., & Bernal-Mizrachi, C. (2010). Implications of vitamin D deficiency in pregnancy and lactation. American journal of obstetrics and gynecology, 202(5), 429.e1–429.e4299. https://doi.org/10.1016/j.ajog.2009.09.002
- Marshall, I., Mehta, R., & Petrova, A. (2013). Vitamin D in the maternal-fetal-neonatal interface: clinical implications and requirements for supplementation. The journal of maternal-fetal & neonatal medicine : the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies, the International Society of Perinatal Obstetricians, 26(7), 633–638. https://doi.org/10.3109/14767058.2012.746306
- Khanna, T., Shraim, R., Zarkovic, M., & Zgaga, L. (2022). Comprehensive Analysis of Seasonal and Geographical Variation in UVB Radiation Relevant for Vitamin D Production in Europe. Nutrients, 14(23). https://doi.org/10.3390/nu14235189
