Importance of Vitamins in Human and Murine Diets

Vitamins are organic molecules that are essential for proper metabolism and bodily function. While they go by different names, most vitamins are actually groups of chemically-related organic molecules known as vitamers¹. Some vitamins must be obtained from dietary sources as they are produced in insufficient quantities or are not synthesized by the body at all. Humans have thirteen essential vitamins that must be obtained from dietary sources:

The Thirteen Essential Vitamins

Vitamin Deficiencies and Overdoses

Vitamin D

Vitamin D is a hormone that aids in calcium absorption. Without it, bones are not able to form correctly.

Vitamin D Deficiency

In the 20^th century, rickets was a very common condition caused by vitamin D deficiency. This condition usually manifested within the first few years of life resulting in stunted growth and bone malformities.

In the 1930s, major food manufacturers began to supplement milk with vitamin D to combat the rickets public health crisis¹. While this condition is not as prevalent today, it is still present in areas with childhood malnutrition and limited access to the necessary medical interventions.

Reduced sun exposure can also result in a slight vitamin D deficiency when there is not enough supplemental vitamin D in the diet. This condition is commonly seen in Northern countries where the sun is not very strong most of the year. Prolonged vitamin D deficiency is a risk factor for the development of chronic disease and overall mortality².

Vitamin D Overdose

Vitamin D is fat soluble. Over-supplementation of this vitamin is not recommended, as a vitamin D buildup in fat cells can cause hypercalcemia, which is a dangerous buildup of calcium in the blood³.

Vitamin C

Vitamin C is essential for the development and maintenance of connective tissues (e.g., collagen, cartilage, bones, and teeth). Additionally, it supports the immune system as well as protects the body from damage due to free radical species by functioning as an antioxidant⁶.

Vitamin C Deficiency

Scurvy is the result of a vitamin C deficiency that has been apparent amongst sea travelers since the 15^th century. The main sources of vitamin C during this time period were fresh fruits and vegetables — none of which were available on multiple month-long journeys while at sea. In the earliest stages, scurvy presents itself as joint pain, under-skin blood spots, and bad breath. As the disease progresses, afflicted people would experience pain too intense to walk and eventually sudden death due to rupturing of the blood vessels⁴.

Vitamin C Overdose

Unlike the fat-soluble vitamin D, over-supplementation of the water-soluble vitamin C does not cause any short-term or long-term harm as it is easily excreted from the body. The role of vitamin solubility will be discussed in depth shortly.

Vitamin A

Vitamin A is important for maintaining immune function, vision, and cellular communication.

Vitamin A Deficiency

A lack of vitamin A is common in regions of the world where access to proper nutrition is not available. Since vitamin A is involved in maintaining immune function, vision, and cellular communication, a Vitamin A deficiency can cause blindness, infertility, stunted growth, and poor wound healing⁵.

Vitamin A Overdose

Much like vitamin D, too much vitamin A can cause dangerous side effects. Vitamin A is fat-soluble and stored in the liver, where the buildup of this compound can cause vision changes, bone swelling, birth defects, and neurological problems⁶.

Importance of Vitamin Solubility

Vitamins are either fat-soluble or water-soluble. The fat-soluble vitamins (A, D, E, and K) are readily stored in adipose tissue or the liver and can, therefore, accumulate in excess amounts if not metabolized. This accumulation can damage the liver, as well as lead to hypervitaminoses and toxic symptoms.

In contrast, water-soluble vitamins must be regularly ingested because they are not stored in the body. These vitamins (8 B vitamins and vitamin C) can be ingested in very high quantities without contributing to toxicity.

The Food and Nutrition Board of the Institute of Medicine at the National Academy of Sciences issues guidelines for the Recommended Dietary Allowance (RDA) of a variety of nutrients including vitamins. Along with the RDA, an Adequate Intake (AI) and Tolerable Upper Intake Level (UL) are also established to ensure nutritional sufficiency and prevent adverse health effects.

Vitamins in the Murine Diet

Vitamins are also essential components of any diet for laboratory mice and rats. For example, the NIH #31M Rodent Diet is a standard chow formulation that contains a vitamin premix with vitamins A, B1, B2, B3, B5, B6, B7, B9, B12, D, K, and E. Of note would be that vitamin C is not added to this diet, as mice and rats can synthesize vitamin C from glucose through L-gulonolactone oxidase enzymatic activity. Some species, including humans, apes, bats, and guinea pigs do not contain a functioning version of this enzyme. Mutant mice lacking a functional L-gulonolactone have been used to study the impact of vitamin C on health. These studies have demonstrated that a lack of vitamin C in the diet can lead to anemia, bleeding, weakness, and eventual death — all symptoms of scurvy⁷.

Effects of Autoclaving on the Murine Diet

The NIH #31M Rodent Diet is autoclavable, which means that it can be exposed to very high pressure and temperature to kill bacteria. While this sterilization process is essential for maintaining the health of the animal, the ingredients in the diet may be degraded. This diet is specifically enriched with heat-labile vitamins including vitamins A, B12, E, thiamine, pantothenic acid and pyridoxine. Steam autoclaving at 121°C for 15-25 minutes reduces the concentrations of these vitamins to levels that are appropriate for the murine diet⁸.

References:

1. Vitamin D -- Health Professional Fact Sheet. National Institutes of Health. (Accessed: 18th July 2019).

2. Nair, R. & Maseeh, A. Vitamin D: The 'sunshine' vitamin. J. Pharmacol. Pharmacother. 3, 118-26 (2012).

3. Marcinowska-Suchowierska, E., Kupisz-Urbańska, M., Łukaszkiewicz, J., Płudowski, P. & Jones, G. Vitamin D Toxicity-A Clinical Perspective. Front. Endocrinol. (Lausanne). 9, 550 (2018).

4. Maxfield, L. & Crane, J. S. Vitamin C Deficiency (Scurvy). StatPearls (StatPearls Publishing, 2019).

5. Villamor, E. & Fawzi, W. W. Effects of vitamin A supplementation on immune responses and correlation with clinical outcomes. Clin. Microbiol. Rev. 18, 446-64 (2005).

6. Chea, E. P. & Milstein, H. Vitamin A. StatPearls (StatPearls Publishing, 2019).

7. Maeda, N. et al. Aortic wall damage in mice unable to synthesize ascorbic acid. Proc. Natl. Acad. Sci. U. S. A. 97, 841-846 (2000).

8. Carter, R. & Lipman, N. Management of Animal Care and Use Programs in Research, Education, and Testing. Second Edition. Boca Raton (FL): CRC Press/Taylor & Francis; 2018. Chapter 27.