• Steven Shuster, MS, CISSN

Nutrition Basics: The Water Soluble Vitamins

Last post we discussed some of the basics about fat soluble vitamins. The other broad category of vitamins is the water soluble vitamins; this includes the B complex vitamins and vitamin C.

Water soluble vitamins differ from fat soluble vitamins in a couple of important ways. The first way is during digestion and absorption: water soluble vitamins are absorbed right into the blood. The second way that they differ is also tied to being water soluble; they are more easily excreted from the body through urine once blood levels reach a certain threshold.

Practically, this means that it is much harder to retain the water soluble vitamins for a long time. The only exception to this is vitamin B12 (cobalamin). Therefore, it is more important to consume the B complex and vitamin C consistently. Fortunately, this is fairly easy and deficiency of these vitamins is very rare in the developed world.

The B complex includes 8 vitamins that mostly share two main functions: helping to release energy and helping to create blood cells and platelets. They perform these functions by acting as coenzymes. That is, they activate or facilitate an enzyme so that the enzyme can catalyze a reaction. They also have some other functions throughout the body.

With the exception of vitamin B12, the B complex vitamins can all be found in both animal and plant (and fungus) sources, so well-rounded vegetarian and vegan diets can still naturally include enough to maintain health.

Vitamin B12 is the exception, it is produced by bacteria and naturally consumed in animal products. Some foods are fortified with vitamin B12, including cereals. Vitamin B12 requirements are the lowest of any micronutrient with a defined need (this is an important caveat because, as we will see in a future post, the ultratrace minerals do not have defined reference intakes). The daily average requirement is less than 1/10 of any other defined requirement!

A healthy body typically recycles vitamin B12 at a very efficient rate so it can take months, years, or even decades before a deficiency results in obvious symptoms.

These days the most common reasons for deficiency of the B complex vitamins are alcoholism and malabsorptive conditions.

Vitamin C is the only water soluble vitamin that is not part of the B complex. Also known as ascorbic acid, vitamin C is most well known for being in citrus fruit, but it is also in asparagus, broccoli, cauliflower, leafy greens, strawberries, and other fruits and vegetables.

Deficiency is rather uncommon in developed nations today. Vitamin C deficiency is well known as scurvy. Fun fact: the British navy sailors were called ‘Limey’ because their rations included lemon juice to help prevent scurvy.

Vitamin C prevents scurvy by performing one of its most important functions, aiding in collagen synthesis. Collagen is a structural protein found in skin, tendons, cartilage and bone.

Vitamin C is responsible for a host of other functions throughout the body. These include, but are not limited to, carnitine synthesis (important in fat metabolism), neurotransmitter synthesis, and antioxidant activity.

It is also suspected that vitamin C may play a role in decreasing risk for cancer, cardiovascular disease, and cataracts.

Though it is not necessary to get the RDA of each water soluble vitamin every day, we are more sensitive to fluctuations compared to the fat soluble vitamins because of the inability to retain (most) for long periods of time.

In our next posts we will turn our attention the other major category of micronutrients, the minerals.

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