In the last 3 posts, I have covered the common cold (rhinovirus), its underlying mechanisms of action, the immunological benefits of vitamin C/quercetin/zinc, and how they inhibit and control viral entry, replication, and inflammatory cascades. In the following sections, I will be considering vitamin D3 as another viable means of supporting the immune system.

D3, also known as cholecalciferol, has become widely known for its ability to correct rickets; a childhood disease characterized by sub-optimal bone development.1 D3 is fairly rare in the diet, but can be found in fatty fish (i.e., sardines, tuna, salmon, swordfish) and to a lesser extent in shitake mushrooms, butter, cheese, eggs, yogurt, and milk.1(389)  D3 is known to play complex roles within the body and supports bone homeostasis (most widely recognized) as well as cell differentiation, proliferation/growth, muscle structure and function.1(393) Please see below links for other benefits of D3 that I have written about previously:

Vitamin D: Types, Utility, Screening, and Optimal Dosing

Determining Optimal Vitamin D3 Levels

Vitamin D3 and Crohn’s Disease

Asthma and Vitamin D

Vitamin D and Essential Hypertension

Vitamin D3 and Prostate Cancer

Vitamin D and Pre-Diabetes

Multiple Sclerosis and Vitamin D3

Vitamin D3 and Inflammation

Vitamin D and Breast Cancer

D3 is a particularly unique substance because of its structure; D3 is a pre-hormone since it contains 3 ring structures (A, C, D).1(389) Once D3 has OH (hydroxyl groups) added to its structure with the help of the liver and kidneys, it becomes 1,25-(OH2)D.2 Most relevantly, 1,25-(OH2)D is considered the biologically active form of D3, making it a hormone; any substance that controls and regulates the activity of target cells and organs.3

Notice (pic below) D3 has 1 OH, but 1,25-(OH2)D has 2 other OH groups added