Vitamin D and your Immune System
When we think about vitamin D, we think of the sun. It’s well known that vitamin D is essential for bone health. Our bodies absorb vitamin D through our skin where it is then stored in fat cells until it is needed to help our bodies absorb calcium from the intestines. When combined with vitamin K, vitamins D3 and K2 synergistically work together to metabolize calcium.
But that’s not all vitamin D does. Research shows that it also plays an important role in supporting the immune system by activating our immune defenses. The immune system’s first line of defense, the killer T cells, can not complete their activation process unless they detect the presence of vitamin D. In addition, studies have shown that vitamin D is associated with lowered cancer risk and plays a critical role in controlling infections and reducing inflammation by triggering antimicrobial pathways that fight against bacterial, fungal and viral pathogens.
In addition, researchers have begun studying the role vitamin D may play in the severity of Covid-19, investigating whether people with vitamin D deficiencies have a weak or abnormal immune response that make them more susceptible to developing Covid-19 and/or experiencing more severe symptoms. However, to date, the research is only observational and requires further study.
Where do we get vitamin D?
- The sun – It takes approximately 15 minutes of sunlight twice a week (depending on the time of year, the latitude of where you live and the pigment of your skin) for our bodies to make enough vitamin D. The middle of the day, when the sun is at its highest point, is the most productive time for your skin to produce vitamin D. The shortened daylight hours of winter and covering our arms and legs limit exposure. If you live at a higher latitude, the low angle of the sun lessons the amount of UVB light produced by the sun that your skin is able to absorb.The temperature of your skin also affects vitamin D absorption. Skin warmed by the summer sun is more efficient at producing vitamin D than cool skin. In addition, the more skin exposed, the more vitamin D the body will make. However, people with dark skin tend to have lower blood levels of vitamin D because their skin pigment acts like shade, reducing vitamin D production. They require more sunlight hours in order to produce sufficient amounts of vitamin D.Note: With the concern of skin cancer, it is important to find the right balance between sun exposure and protection.
- Specific types of mushrooms – Portobellos, mistake, morel, button and shiitake all naturally contain vitamin D.
- Fortified foods and plant-based milks – Read your food labels. Some foods, such as tofu and plant-based milks, are fortified with vitamin D.
- Supplements – Vitamin D supplements are easily absorbed in the body. Because vitamin D is fat-soluble, it’s important to take it with food. It’s also best to take vitamin D in the morning due to its connection with lower levels of melatonin, a hormone that regulates sleep. Taking vitamin D in the morning allows your body to synthesize the vitamin at a time when your melatonin levels are naturally lower so it wont interfere with your melatonin production needed for sleep.Important: Not all vitamin D supplements are vegan. There are two types of vitamin D: D2 and D3. Vitamin D2 is created through the ultraviolet irradiation that comes from plants and fungi (vegan sources). Vitamin D3 is typically made by the ultraviolet irradiation from sheep’s wool (not vegan) or lichen (vegan). D2 and D3 are both effective forms of vitamin D.Note: When purchasing supplements, it is important to make sure that the supplement company uses third party quality control testing and clearly identifies the nutrient sources.
What Inhibits Vitamin D Absorption?
- Age (65 years and older)
- Darkness of your skin pigmentation
- Health of your gut, liver and kidneys
- Latitude where you live
- Limited sun exposure
- Temperature of your skin
Vitamin D Toxicity
Too much vitamin D causes a buildup of calcium in your blood which can result in nausea, vomiting, weakness, frequent urination, kidney stones, etc. Absorbing too much vitamin D through sun exposure or consuming vitamin D rich foods is unlikely as your body regulates what it absorbs. However, when taking vitamin D supplements, there is always a risk of overdosing. But it takes large doses of vitamin D to reach toxic levels (around 60,000 IUs a day over several months).
The Food and Nutrition Board (FNB) currently recommends 600 IUs of vitamin D a day for ages 1 – 70 and 800 IUs a day for those over 70. However, it is important to speak to your medical practicitioner before adding any supplements to your diet.
Testing Vitamin D Levels
There are two forms of vitamin D in our bodies; the active and inactive forms. In the bloodstream, both vitamin D2 and D3 change into 25 hydroxyvitamin D (25OH) D, the inactive form of vitamin D that is stored in your body waiting to be needed and activated. The standard blood test physicians use to determine your level of vitamin D only detects this inactive form.
Currently, it is unclear whether it is helpful for everyone to be routinely tested for vitamin D deficiency as the standard blood test ordered by physicians does not show how well your body is able to metabolize vitamin D into the active form. As a result, vitamin D testing is currently used to screen or monitor bone disorders and chronic illnesses and is recommended for those with minimal exposure to sunlight.
If you feel you have cause for concern about your vitamin D levels, talk with your medical practitioner to find out if testing is right for you and how to interpret the results based on your medical history.
Sources and suggested further reading:
- 5 ways to increase your vitamin D intake, PETA (2015)
- Exploring the links between coronavirus and vitamin D, by Anahad O’Conner, The New York Times (2020)
- Is Vitamin D Harmful Without Vitamin K?, by Atli Arnarson BSc, PhD, Healthline (2017)
- The Nutrition Source: Vitamin D, Harvard School of Public Health (2020)
- Vitamin D and Aging, by Dr. J. Christopher Gallagher, NCBI (2013)
- Vitamin D crucial to activating immune defenses, University of Copenhagen, Science Daily (2010)
- Vitamin D Myths ‘D’-bunked, by Colleen Moriarty, Yale Medicine (2018) –
- Vitamin D study sheds light on immune system effects, University of Edinburgh, Science Daily (2019)
- Vitamin D Tests, Lab Tests Online, AACC (2021)