With all the hype about vitamin D going on, it can be hard to separate facts from fiction.
How much vitamin D do I need? How to get enough vitamin D? Which are the best food sources? Do I need a vitamin D supplement and which one?
If you’ve been asking any of these questions (or all of them), ask no further.
This article covers everything you need to know about vitamin D—health benefits, recommendations, sources, and useful tips. You will even learn some surprising and fun facts about the “sunshine vitamin”.
What is vitamin D?
Vitamin D stands for a group of steroid compounds that play crucial roles in our mineral absorption, immunity, and mental health.
The two main forms are vitamins D2 (ergocalciferol) and D3 (cholecalciferol). We ingest both types through food, but our main source of vitamin D is sunlight.
Our bodies primarily use vitamin D3; it undergoes two transformations in the liver and kidneys to form a biologically active calcitriol (1,25-dihydroxy-vitamin D3).
Did you know?
Technically, vitamin D is not a vitamin.
Dietary intake of vitamin D is not essential since we can synthesize it from sun exposure. Given its structure and mechanism of action, we can consider vitamin D a hormone. Calcitriol binds to a specific vitamin D receptor (VDR), which acts as a transcription factor (controls our gene expression).
Learn about food and exosomes!
What are the roles of vitamin D in our body?
Vitamin D is essential for our physical and mental health as it:
- Regulates calcium absorption
- Maintains strong immunity
- Helps in brain development
- Controls anti-cancer genes and much more
Vitamin D is the key factor for proper calcium metabolism and healthy bones. It stimulates our body to absorb more calcium and send it to our skeleton. Before food fortification with vitamin D, osteomalacia and rickets (soft bones) were affecting a large percentage of the human population; third-world countries are still dealing with this issue.
Plenty of research connects vitamin D status and immunity. This study reveals: it can activate human T cells and help them remove “intruders” from our body. A study published in the American Journal of Clinical Nutrition showed that “vitamin D3 supplementation during the winter may reduce the incidence of influenza A”.
Vitamin D influences our genes and may prevent cancerous mutations. American Journal of Public Health published a review of 63 studies on vitamin D and cancer risk. The authors regarded vitamin D supplementation as an effective strategy to prevent different types of cancer.
Sunshine makes you happy, right? Here’s the science behind it: vitamin D plays an important role in our mood regulation and mental health. Seasonal affective disorder is caused by vitamin D deficiency during winter. In the absence of sunshine, vitamin D supplements can get you through the day (or a few months). They significantly improve the symptoms of depression, according to this meta-analysis of 15 studies.
How to get enough vitamin D?
You will see many different recommendations for vitamin D intake. The following table shows the official Recommended Dietary Allowance (RDA) values for Vitamin D:
| Recommended Dietary Allowances (RDAs) for Vitamin D | ||||
| Age | Male | Female | Pregnancy | Lactation |
| 0–12 months* | 400 IU (10 mcg) | 400 IU (10 mcg) | ||
| 1–13 years | 600 IU (15 mcg) | 600 IU (15 mcg) | ||
| 14–18 years | 600 IU (15 mcg) | 600 IU (15 mcg) | 600 IU (15 mcg) | 600 IU (15 mcg) |
| 19–50 years | 600 IU (15 mcg) | 600 IU (15 mcg) | 600 IU (15 mcg) | 600 IU (15 mcg) |
| 51–70 years | 600 IU (15 mcg) | 600 IU (15 mcg) | ||
| >70 years | 800 IU (20 mcg) | 800 IU (20 mcg) | ||
- Adequate Intake (AI); Conversion : 1 µg = 40 IU and 0.025 µg = 1 IU)
Source: National Institutes of Health
Our skin produces vitamin D3 when exposed to sunlight. When UV-B light hits the skin surface, they transform 7-dehydrocholesterol into vitamin D3. A fair-tanned person needs 15-20 mins of sun exposure to produce the required daily amount. How well your body will synthesize vitamin D depends on many factors such as:
- Skin color (dark skin requires longer exposure)
- Location (the closer to equator, the better production)
- Time of the day (hot sunshine=better production)
- Exposed surface
Did you know? Rays of UV-B light must hit your skin above a certain angle for the synthesis to occur. That’s why sun exposure around noon yields the biggest amounts of vitamin D.
Vitamin D food sources
Some foods contain vitamin D but we can’t rely on them to provide the recommended amounts. Best food sources of vitamin D3 are:
- Salmon, cooked (100g=522IU)
- Tuna, canned (100g=269IU)
- Egg yolk, cooked (1 egg=44IU)
- Beef liver, cooked (100g=49IU)
Vitamin D from these foods is very important during the not-so-sunny months. Considering the limited sources, however, you should add a high-quality vitamin D3 supplement.
Vitamin D for vegans
Plant foods don’t contain vitamin D3 but mushrooms can provide significant amounts of vitamin D2. Just like we make vitamin D from sunlight, mushrooms do the same. When exposed to UV light, they produce much bigger amounts. This awesome feature brings you a vegan-friendly vitamin D food source. One cup of UV-treated mushrooms contains 800-1100IU of vitamin D2 (source).
TIP: Sun-drying increases mushrooms’ vitamin D content. You can dry a bunch of mushrooms during summer and freeze them. Add a handful to any dish for an extra vitamin D supply when the sun is gone.
The majority of fortified foods (cereals, juices, plant milk) also contains vitamin D2. Same goes for vegan-friendly supplements since vitamin D3 comes only from animal sources. Though both forms produce similar effects in our body, vitamin D3 is much more potent; it directly converts into calcitriol. Vegans can bridge the cloudy periods with mentioned vitamin D2 sources but the evidence favor vitamin D3.
This doesn’t mean you can’t get too much sun exposure. Avoid getting sunburned as it can lead to skin problems (and painful sleepless nights).
Exposure to UV lamps can also stimulate the vitamin D3 production. This “supplement” could provide the more potent form to strict vegans and people with malabsorption (inability to absorb vitamin D from food). Experts from the Vitamin D Council recommend using UV lamps during winter. Remember, UV-B light (not UV-A) helps you produce vitamin D.
In this short video, Dr. Axe reveals the signs and symptoms of vitamin D deficiency:
When using a vitamin D supplement, make sure you follow the optimal intake guidelines. Vitamin D overdose can drastically increase the calcium levels and damage the kidneys, liver, and heart. According to the Endocrine Society, a safe upper level for vitamin D is 4000 IU/day.
Did you know? You can overdose on vitamin D from supplements, but not from sun exposure. For most of us, it takes less than 30 mins to produce the required amount. When our body hits the limit, it degrades the excess vitamin D and turns it into other compounds.
Summary
- Vitamin D is crucial for our bones, immunity, and mental health
- A healthy adult requires 600IU (15mcg) of vitamin D daily
- The main source of vitamin D is sun exposure (15-30 mins/day)
- Foods have limited amounts of vitamin D3 (animal sources) and D2 (mushrooms)
- Experts recommend supplementing vitamin D during the winter
- Vitamin D3 is more potent, while vitamin D2 is vegan-friendly
References
- de Lourdes Samaniego-Vaesken, M., Alonso-Aperte, E. and Varela-Moreiras, G. (2012). Vitamin food fortification today. Food & Nutrition Research, 56(1), p.5459. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3319130/
- von Essen, M., Kongsbak, M., Schjerling, P., Olgaard, K., Ødum, N. and Geisler, C. (2010). Vitamin D controls T cell antigen receptor signaling and activation of human T cells. Nature Immunology, 11(4), pp.344-349. https://www.ncbi.nlm.nih.gov/pubmed/20208539
- Urashima, M., et al. (2010). Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. The American Journal of Clinical Nutrition, 91(5), pp.1255-1260. https://www.ncbi.nlm.nih.gov/pubmed/20219962
- Garland, C., et al. (2006). The Role of Vitamin D in Cancer Prevention. American Journal of Public Health, 96(2), pp.252-261. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1470481/
- Spedding, S. (2014). Vitamin D and Depression: A Systematic Review and Meta-Analysis Comparing Studies with and without Biological Flaws. Nutrients, 6(12), pp.1501-1518. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4011048/
- Ods.od.nih.gov. (2016). Office of Dietary Supplements – Vitamin D. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
- Ndb.nal.usda.gov. Food Composition Databases Show Nutrients List. https://ndb.nal.usda.gov/ndb/nutrients/report?nutrient1=324&nutrient2=&nutrient3=&fg=&max=25&subset=0&offset=0&sort=c&totCount=5425&measureby=m
- Tripkovic, L., et al. (2012). Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. The American Journal of Clinical Nutrition, 95(6), pp.1357-1364. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3349454/
- Vitamin D Council. (2018). UV light in the wintertime. https://www.vitamindcouncil.org/uv-light-in-the-wintertime/
- Ross, A., et al. (2011). The 2011 Report on Dietary Reference Intakes for Calcium and Vitamin D from the Institute of Medicine: What Clinicians Need to Know. The Journal of Clinical Endocrinology & Metabolism, 96(1), pp.53-58. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3046611/
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