Why You Need Vitamin D For A Stronger Immune System

By: Alexa Nicole Fiffick, DO, MBS • Posted on January 04, 2022

Why You Need Vitamin D For A Stronger Immune System

There is a lot of key research regarding the importance of Vitamin D, the so-called sunshine vitamin. We have known for some time that vitamin D levels drop in the winter, especially the farther one is away from the equator and direct sunshine.

Low vitamin D levels can lead to an increase in respiratory infections amongst other conditions including seasonal depression, arthritis, multiple sclerosis and increased risk of some cancers. With COVID-19 cases increasing and the winter having arrived, you probably should get acquainted with this miracle, pro-sterol hormone vitamin D3 - that is not actually a true vitamin.

How much vitamin D should I be getting? More than you think!

Does my multivitamin have enough vitamin D? Probably not if you are over 40 and live in a northern climate. The darker the skin and the higher the body weight folks may have lower levels.

What do I do if my level is low? Increase your intake under your physician’s guidance.

What is Vitamin D?

  • Vitamin D is not a vitamin, unlike vitamin C or B12 which are true vitamins. Vitamin D is something your body can NEVER make and thus you have to ingest it in your diet.
  • Vitamin D is a pro-steroid hormone that helps with calcium and phosphate absorption. Thus, it is important for building and maintaining healthy bones in all stages of human life, including in-utero. It affects cell signaling and immunity as well.
  • Vitamin D is important for prevention and/or treatment of postmenopausal bone loss.

Vitamin D deficiency

According to many lines of evidence, vitamin D deficiency is associated with the following:

  • colon cancer
  • prostate cancer
  • breast cancer
  • diabetes
  • high blood pressure
  • arthritis
  • multiple sclerosis

Vitamin D and the Immune System

However, more recently, vitamin D has been found to have a potentially significant impact on the immune system. It helps your cells communicate with each other and it has been found that all cells in the immune system have vitamin D receptors. In particular, immune cells called T-cells, of which there are many kinds that perform different roles, can be activated or suppressed by Vitamin D. Thus, it plays a role in both autoimmune conditions and infectious disease, including Covid-19.

There have even been studies that show that vitamin D supplementation can reduce upper respiratory tract infections.

How is Vitamin D Related to COVID?

Since the beginning of the COVID-19 pandemic, studies have been investigating how vitamin D has a role in COVID outcomes. Studies that look back on patients that are hospitalized for COVID infections versus those that can remain at home for their recovery show lower levels of serum vitamin D. Some randomized controlled trials have even shown a higher rate of respiratory support in those with low vitamin D and a longer ICU stay in those with low vitamin D.

A recent meta analysis of 54 clinical studies demonstrated that patients with low vitamin D levels are at an increased risk of Acute Respiratory Distress Syndrome, ICU admission and mortality from COVID-19.

What does this mean? Patients with sufficient vitamin D levels (levels 50-55) are likely to have better outcomes if infected with SARS-Cov2 than those with insufficient or deficient amounts.

How Much Vitamin D3 Do You Need?

The American Endocrine Society and the National Osteoporosis Foundation provide guidelines for your doctor to discuss recommendations regarding vitamin D intake with you.

  • The basic recommendation for any adult person under 50 years old should get 400-800 international units (or Iu’s) per day, which for many folks is simply too low to maintain a level of over 50.
  • The recommendation for people over age 50 should get at least 800-1,000Iu’s per day. Specifically, vitamin D3 (cholecalciferol) is the recommended form of this vitamin.

3 ways to get vitamin D

  1. Sunlight
  2. Food
  3. Supplements/medications

Now that winter is here, sunlight is less available and travel is becoming more difficult, so ingesting enough vitamin D from food or supplements is even more crucial. Furthermore, it is still difficult to get all the needed vitamin D3 from foods - unless you eat like an Eskimo! The foods to add to your diet that are rich in vitamin D include:

  • fatty fish
  • beef liver
  • fortified milk (cow, soy)
  • egg yolks
  • fortified orange juice
  • fortified cereals

Even then, you probably will not meet your daily intake goal. We recommend you estimate your daily intake and consider over the counter supplements to reach your daily goal.

How do I know if I’m getting enough vitamin D3?

The easiest way to find out if what you are eating and absorbing from calcium is enough is to talk to your doctor. They can order a simple blood test to see if your level is sufficient, which is typically >31ng/mL for bone but for optimized immunologic health many physicians recommend a level over 50 ng/mL. If your levels are low, you may need a loading dose of daily 10,000iu vitamin D3 for a few months with recheck. If the level is <12ng/mL, you may need further testing to see why that level is deficient, such as bowel disease, celiac disease or parathyroid disease.

Does my multivitamin have enough Vitamin D?

Unfortunately, most over-the-counter vitamins do not often have enough vitamin D3 to reach daily goals. Talking to your doctor and choosing a sufficient dose of separate Vitamin D is important for overall immune function, disease prevention and bone health. Talk to your doctor today if you want to know what your vitamin D level is and take charge of your health.

Be Strong, Be Healthy, Be in Charge!
- Alexa Fiffick, DO

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About Alexa Nicole Fiffick, DO, MBS

Dr. Alexa Nicole Fiffick is a Board Certified Family Medicine physician. She is a first year clinical Specialized Women’s Health Fellow at the Cleveland Clinic Center for Specialized Women’s Health.

Dr. Fiffick was born and raised in Greater Cleveland, Ohio. She graduated from Case Western Reserve University in 2012 with a Bachelor’s in Sociology with minors in Dance and Chemistry. She achieved a Master’s in Biomedical Science at The Commonwealth Medical College in 2013. She spent a year working in research at the Cleveland Clinic. Then, she went to medical school at Alabama College of Osteopathic Medicine, graduating in 2018.

Dr. Fiffick graduated from Doctors Hospital Family Medicine program for residency, with a certified focus on Women’s Health. She spent time working with underserved communities via Mobile Medicine in residency. Through this she fell in love with caring for underserved women and women in mid through later life.


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