What Does Vitamin D Do for Us and Where Do We Get It?

Written: May 2022

Vitamin D consists of a group of fat-soluble secosteroids, a type of steroid. Vitamin D has several positive biological effects. It increases intestinal absorption of calcium, magnesium, and phosphate. Vitamin D also regulates numerous cellular functions in your body. Its anti-inflammatory, antioxidant, and neuroprotective properties support immune health, muscle function, and brain cell activity. A simpler view of Vitamin D is as a nutrient your body needs for building and maintaining healthy bones. Without vitamin D your bones cannot absorb enough calcium resulting in bones becoming brittle, soft, and thin leading to osteoporosis. Research on vitamin D has found it can have positive effects in a wide-ranging set of conditions including cancer, cognitive health, multiple sclerosis, osteomalacia, osteoporosis, psoriasis, and rickets.

The importance of the vitamin raises the question of where we get it. One source is our body. It can produce vitamin D when direct sunlight converts a chemical in our skin into calciferol which is an active form of vitamin D. The amount of vitamin D our skin produces depends on many factors, including the time of day, season, latitude, and our skin pigmentation. If you live in a place which does not get much sun or your lifestyle keeps you indoors, vitamin D production might decrease or even be completely absent. Dermatologists properly tell us to stay out of the sun to prevent skin cancer, but the result can be a decrease in vitamin D production.

How about what we eat? Vitamin D is not found naturally in many foods. Plants are generally poor sources of the vitamin. Most people rely on animal products such as dairy, eggs, and meat. Other sources include fatty fish such as mackerel, salmon, or sardines and from fortified milk or fortified cereal. A new source of vitamin D may be on the horizon.

Researchers are finding gene-edited tomato plants produce a precursor to vitamin D which may provide an animal-free source of the essential vitamin. When the gene-edited tomatoes are exposed to ultraviolet light in the laboratory, some of the precursor, called provitamin D3, is converted to real vitamin D3.[1] It may be quite a while before the discovery is commercialized. One big test is whether the modified plants will thrive when grown outside. Other obstacles include regulatory approvals and consumer acceptance. Both are iffy at this point.

A simple blood test can check your level of vitamin D. If you don’t have enough vitamin D from sunlight or dietary sources, a plan B, or D, would be vitamin D supplements. Taking a multivitamin with vitamin D may help improve bone health. Your doctor can recommend a daily amount of vitamin D ranging from 400 international units (IU) to 800 IU depending on your age. With as many as one billion people believed to be without enough vitamin D, we need all the sources we can find.

[1] Jie Li et al., “Biofortified Tomatoes Provide a New Route to Vitamin D Sufficiency,” Nature Plants  (2022).