“Cell Defenses and the Sunshine Vitamin” Article Summary [Biology notes]

As part of our unit on human nutrition for IB Biology, we were asked to read and summarize an article from Scientific American on the effect of Vitamin D on human cells and its relation to human diseases. The following is a relatively succinct one page summary of the article:

This article explores the formation and usage of Vitamin D, and the potential problems that might result when Vitamin D is not produced in sufficient amounts.

Some historical ailments were linked to a deficiency of Vitamin D, or could be treated with Vitamin D. Examples of these ailments include tuberculosis and rickets. No one understood why exposure to sunshine mysteriously healed many victims of these diseases. By the early 20^th century, experiments were conducted which determined that irradiated skin shared a common element with cod-liver oil (a popular antirickets medicine): vitamin D. Thus, a link was drawn between Vitamin D, exposure to sunshine, and the mysterious ailments previously mentioned. However, it was not understood how skin exposure to sunshine managed to produce Vitamin D.

Additional research determined that the skin is the only organ that produces Vitamin D from sunshine, and it does so through a variety of steps. The ultraviolet rays in sunlight interact and break down 7-dehydrochlolestrol molecules, which creates Vitamin D₃. Vitamin D₂ can be found in foods, and acts in a similar way to D₃ in this case. The liver then converts it into 25-hydroxyvitamin D (25D), which then reenters the bloodstream. Most of the 25D in the bloodstream is converted into 1,25D in the kidneys. Recently it has been found that other organs can convert the 25D in the bloodstream into the active 1,25D.

The active form, 1,25D, affects the physiology of many different organs and cell types. It is most well known for its bone-building abilities, but new evidence suggests that it has potent anticancer actions and serves as an important regulator in the immune system. It is also known for its ability to turn genes “on” or “off” in the human body regardless of the tissue. There is a protein called the Vitamin D receptor (VDR) which is a transcription factor in the cell’s nucleus; this allows 1,25D to regulate about 1000 different genes. When 1,25D bonds to VDR and attaches to the retinoid-x receptor (RXR), the resultant complex is able to produce a protein through the cellular machinery. Arguably, it could be called a hormone since it is produced in one tissue and affects other tissues. It indeed belongs to the nuclear receptors family of proteins. In essence, 1,25D has a wide range of potential effects.

The synthetic counterpart of 1,25D, called EB1089, has similar benefits. In experiments with animals, it has been found that this compound has been able to reduce tumour growth by about 80%, and reduce cell reproduction rates by altering some genes. It is possible that the body creates Vitamin D in order to counteract extended exposure to the sun and consequently UV radiation. It also appears that 1,25D can also act as an anti-inflammatory agent.

However, it has been discovered that a significant portion of the world’s population, particularly people in temperate regions, are not receiving enough Vitamin D, which prevents them from receiving the full extent of Vitamin D’s benefits. For those in temperate regions, obtaining Vitamin D through dietary means is critical, since the lack of sunlight at some times of the year (eg. winter) can cause severe Vitamin D deficiencies. Although consuming food is less efficient than exposure to sunshine in terms of Vitamin D, there are still some foods with significant amounts of Vitamin D, such as cod-liver oil, shiitake mushrooms and cooked tuna. Common Vitamin D foods can provide about 20-1600 IU of Vitamin D₂ or D₃, but a mere 15-20 minutes of exposure to sunshine can produce 10000 IUof D₃. For about half of US adults, at least 1000 IU of Vitamin D₃ need to be consumed daily in order to reach the minimum healthy level for Vitamin D. Essentially, drastic action must be undertaken in order to combat this grave deficiency epidemic.

Long-term Vitamin D deficiencies, even if it just a minor deficiency, can increase frequency of bone fractures and vulnerability to autoimmuine/infectious diseases. If the public consumed the Vitamin D it needed daily, then the general health of the people would increase greatly.

The original article from Scientific American is for subscribers, but the link has enough of an excerpt to give you a sense of what the article is like.