March 25, 2021

Optimizing the Immune System by Consuming Leafy Greens

Jonathan Valdez

By Jonathan Valdez, MBA, RD

March is National Nutrition Month. With Spring here and an end to the pandemic in sight, what better time to talk about how consuming leafy greens can optimize our immune systems.

Leafy green vegetables are nutritious and easy to add to various dishes such as smoothies, stir-fries, and salads to name a few. The vitamins and minerals within them are key to the immune system. Specifically, vitamin C and vitamin A are two of the most important vitamins in keeping the immune system up and running. 

Vitamin C

Why do we all seem to have this belief that taking vitamin C will prevent us from getting a cold? Well, it’s all thanks to a famous two-time Nobel Prize winner, Linus Pauling. In 1970, he published a book titled, “Vitamin C and the Common Cold”, stating vitamin C can prevent people from getting a cold1. While this isn’t completely true, Linus Pauling was onto something. 

People with higher levels of vitamin C have less severe allergy symptoms and acute respiratory infections, like pneumonia. Vitamin C is essential in normal lung function. It has also been found that 200mg of Vitamin C a day will decrease the severity and duration of cold symptoms2

Want more vitamin C in your diet? Try red and green cabbage! Just one cup of red cabbage a day provides about 44% of your daily recommended vitamin C and green cabbage about 28%3. These will both taste great in a salad or a corned beef and cabbage recipe.









Vitamin A

In the body, there is a form of vitamin A called retinoic acid, which can act as a hormone. Hormones are like small messages in the body, similar to an email. They tell organs in the body how things are going and what changes they need to make. The immune system relies heavily on hormones to manage how it functions. Retinoic acid increases T-cells and B cells in the body4,5. T-cells are a type of white blood cell that acts as a soldier for the body, eliminating foreign objects, while the B cells are responsible for activating the T-cells. Studies have shown that people who are deficient in vitamin A are more likely to die from gastrointestinal and respiratory infections4. Another function of vitamin A is providing relief of autoimmune inflammation in conditions like arthritis and psoriasis5

Vitamin A is also a fat-soluble vitamin. Better absorption of vitamin A occurs when it is eaten along with fat. Experts recommended consuming 1 teaspoon of fat at meals that contain foods rich in fat-soluble vitamins. But let’s be real, that’s not going to cover a whole salad! So, try mixing a teaspoon of fat (dressing, olive oil, etc.) with 1 tablespoon of fat-free dressing. Having a smoothie? Add in a small amount of healthy fats such as peanut butter or nuts to get the most out of your leafy greens! 

The best leafy greens for vitamin A? One cup of romaine lettuce provides about 23% of your daily recommended intake and One cup of spinach provides about 16%6! Add these leafy greens to a salad, smoothie, or sauté them with a little salt and pepper as a side dish. 










  1. Biographical Overview | Linus Pauling – Profiles in Science. (2019, March 12). Retrieved April 16, 2020, from
  2. Carr, A. C., & Maggini, S. (2017). Vitamin C and immune function. Nutrients, 9(11), 1211.
  3. Office of Dietary Supplements – Vitamin C. (2019, December 10). Retrieved April 17, 2020, from
  4. Mora, J. R., Iwata, M., & Von Andrian, U. H. (2008). Vitamin effects on the immune system: vitamins A and D take centre stage. Nature Reviews Immunology, 8(9), 685-698.
  5. Larange, A., & Cheroutre, H. (2016). Retinoic acid and retinoic acid receptors as pleiotropic modulators of the immune system. Annual review of immunology, 34, 369-394.
  6. Office of Dietary Supplements – Vitamin A. (2020, February 14). Retrieved April 17, 2020, from