Vitamin D, also known as “the sunshine vitamin”, is a fat-soluble vitamin that helps the body absorb calcium and phosphate, which are essential for the formation of bones and teeth, the function of the heart, muscles and nerves, and for cell and tissue repair. In this article, you will learn more about vitamin D, including why we need it, where we get it, and what happens if we do not have enough of it.
What are vitamins?
Vitamins are substances that are necessary for the normal cell function and good health. There are 13 essential vitamins that can be divided into two categories: fat-soluble and water-soluble. Vitamin D, along with vitamins A, E and K, is fat-soluble, which means it is more easily absorbed in the presences of dietary fat. The other vitamins, C, B1 (thiamine), B2 (riboflavin), B3 (niacin), B5, B6, B7 (biotin), B9 (folic acid), B12 are water-soluble and any excess in the body is excreted in urine. Each vitamin has a specific function, and it is important to get enough of each one .
What does vitamin D do?
Vitamin D helps the body absorb calcium and maintain blood levels of calcium and phosphate, which are essential for the formation of bones and teeth, the function of the heart, muscles and nerves, and for cell and tissue repair. Additionally, its anti-inflammatory, antioxidant and neuroprotective properties support immune health, muscle function and brain cell activity.
Vitamin D is critical for promoting bone health and preventing or treating osteoporosis, osteomalacia and rickets. Through its many roles that include glucose metabolism, vitamin D is currently being investigated for its positive impact on type 2 diabetes and weight loss, cancer, cardiovascular diseases, depression, and multiple sclerosis. Several studies are underway to evaluate the role of vitamin D and its part in preserving good health.
Sources of vitamin D
Sun exposure is the main source of vitamin D. The body produces the vitamin when the skin is exposed to direct ultraviolet (UV) radiation from the sun through a chemical reaction that converts a substance, 7-dehydrocholesterol, into vitamin D3. For most people with light skin, 10 to 15 minutes of sunshine three times a week is enough to produce the required amount of vitamin D [1, 2]. However, synthesis of vitamin D by the skin can be affected by season, amount of cloud, geographical location, age, skin color and sunscreen use, meaning some people will not be able to produce enough vitamin D this way .
Vitamin D is naturally present in several foods in two forms. Vitamin D2, is found mainly in plant-based food, and vitamin D3, which is made by the body and can be found in animal-based food.
Sources of vitamin D:
- Fatty fish (salmon, mackerel, herring and tuna)
- Cod liver oil
- Egg yolks
- Liver and red meat
- Fortified cereals
- Fortified milk and dairy products
How much vitamin D do I need?
The recommended daily amount of vitamin D depends on the person’s age. Always consult with your healthcare provider regarding your daily intake of vitamin D.
Vitamin D deficiency
Vitamin D deficiency affects ~40% of the European population, and it is estimated that 13% of Europeans are severely deficient in vitamin D . This occurs when people consume lower than recommended levels of vitamin D, have limited exposure to sunlight, kidneys have difficulty converting the vitamin to its active form, or the digestive system does not sufficiently absorb vitamin D from food.
Groups that are at higher risk for vitamin D deficiency include
- People following a vegetarian or vegan diet
- Breastfed infants
- The elderly
- People with limited sun exposure, e.g., those who do not often go outside or cover-up in the sun
- People with dark skin
- People with obesity or who have had gastric bypass surgery
- People with kidney disease
- People with certain conditions that limit fat absorption, such as cystic fibrosis, celiac disease, Crohn’s disease, ulcerative colitis, or liver disease
Symptoms of vitamin D deficiency
Although many people with vitamin D deficiency do not have symptoms, they can occur and may include regular sickness or infection, fatigue and changes in mood, bone and back pain, impaired wound healing, hair loss and muscle pain. If deficiency continues for long periods, it may result in complications leading to severe health disorders. In infants and children, vitamin D deficiency may cause rickets, a disease characterized by failure of bone tissue to become properly mineralized, resulting in soft, weak, deformed and painful bones. In teens and adults, vitamin D deficiency can lead to osteomalacia, a disorder that causes bones to soften, leading to bone pain and muscle weakness.
Vitamin D supplements
It is not easy to get enough vitamin D from food, and most people rely on sun exposure to obtain the required amount. This means that in autumn and winter, when there is less sun, most people will benefit from a vitamin D supplement . Your healthcare provider can advise you.
While low levels of vitamin D affect bone health and growth, high levels of vitamin D can also be toxic. The following symptoms may indicate intake of vitamin D above recommended levels :
- Nausea and vomiting
- Poor appetite and dry mouth
- Weight loss
- Weakness and confusion
Over time, hypercalcemia (calcium build up) can cause over calcification of bones and hardening of blood vessels, kidney, lung, and heart tissues, resulting in kidney stones and kidney damage and disturbances in heart rhythm [5, 6].
Always consult your healthcare provider prior to and while taking supplements.
Measuring vitamin D levels
Screening for vitamin D status is becoming a common part of routine laboratory blood testing and is the best way to know if a person has sufficient levels of vitamin D. The test is performed via a blood draw, and the sample is then analyzed in the laboratory to calculate the levels of vitamin D in the blood.
Vitamin D is essential for good health. Individuals should meet and maintain their vitamin D needs at an acceptable level through healthy diet and by spending time in the sun ― which should be done with caution as sun exposure is a risk factor for developing skin cancer. Taking vitamin D supplements or having a higher risk for vitamin D insufficiency requires regular monitoring of vitamin D levels. By researching and getting information from healthcare professionals regarding vitamin D and the significant role it plays in good health, individuals may find a balance and maintain normal vitamin D levels.
The content of this article is for informational purposes only and is not intended to replace medical advice. Please visit your healthcare provider if you have concerns about your health and well-being.
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 “Vitamin D. Fact Sheet for Health Professionals.” National Institutes of Health (NIH), Updated 12 Aug. 2022 https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/. Accessed 13 Jul. 2023.
 Amrein, Karin, et al. “Vitamin D deficiency 2.0: an update on the current status worldwide.” Eur J Clin Nutr 74, 1498–1513 (2020). https://doi.org/10.1038/s41430-020-0558-y.
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