Vitamin D is an important nutrient that plays a role in maintaining overall health, particularly in the absorption of calcium and phosphorus for strong bones. It also supports immune function and cell growth. While D2 and D3 are widely recognized for their biological significance, the mention of “Vitamin D5” can lead to questions. This article explores what Vitamin D5 is and why it is not typically included in discussions or supplements.
The Various Forms of Vitamin D
The term “Vitamin D” collectively refers to a group of fat-soluble compounds known as secosteroids. These compounds share a similar basic structure but differ in their side chains, leading to various numbered forms, including D1 through D7. Among these, ergocalciferol (Vitamin D2) and cholecalciferol (Vitamin D3) are the most prominent and biologically active forms relevant to human health.
Vitamin D2 is primarily found in plant sources, such as certain mushrooms, and is often used to fortify foods. Vitamin D3, on the other hand, is produced in the skin upon exposure to ultraviolet B (UVB) radiation from sunlight, and it is also present in some animal products like fatty fish, egg yolks, and beef liver. Both D2 and D3 are converted in the body, first in the liver and then in the kidneys, into their active forms to perform their functions.
Focus on Vitamin D5
Vitamin D5 is known chemically as sitocalciferol. Unlike the more common D2 and D3, Vitamin D5 is considered a synthetic form of vitamin D, meaning it is not typically found in significant quantities in natural food sources or produced by the human body. Its chemical structure is derived from sitosterol, a plant sterol.
Research into Vitamin D5 is considerably limited when compared to the extensive studies conducted on D2 and D3. While some studies have explored its properties, particularly in the context of potential medicinal applications, it has not emerged as a significant player in human nutrition or common supplementation. For instance, a derivative of Vitamin D5 has been investigated for its potential anti-tumor effects, noting it did not cause hypercalcemia, a side effect associated with high doses of Vitamin D3.
Why Vitamin D5 is Not Commonly Discussed
Vitamin D5’s synthetic nature is a primary reason for its obscurity in general nutritional discussions. It is not naturally abundant in the diet nor is it produced by the skin like Vitamin D3. This contrasts sharply with Vitamin D2 and D3, which are readily available from natural sources or through sun exposure.
The biological activity of Vitamin D5 in the body is significantly lower than that of Vitamin D3. Studies have shown that Vitamin D5 is considerably less effective at promoting calcium absorption and bone calcification compared to D3. For instance, research indicates Vitamin D5 is significantly less active than Vitamin D3 in these processes.
The lack of robust scientific research supporting its efficacy or benefits in human health also contributes to its non-prominence. The focus of nutritional science and public health remains on Vitamin D2 and D3 due to their proven roles and widespread availability. Consequently, Vitamin D5 is not commonly used in dietary supplements or fortified foods, as the established forms provide the necessary health benefits.