Vitamins: Health Benefits and Risks

Vitamins are organic (non-mineral) compounds essential to the proper functioning of the human body, but the amounts required are minimal.

Vitamins fall into two main groups:

• Water-soluble vitamins include ascorbic acid (vitamin C) and the B-group vitamins, such as thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B8), folate (B9) and cobalamin (B12). These vitamins dissolve in water and are eliminated through urine. With the exception of vitamin B12, they are not stored in the body.
• Fat-soluble vitamins include vitamins A, D, E and K. These vitamins dissolve in fats and, as our bodies have natural fat reserves, they can be stored in the body.

Our bodies cannot synthesize the various vitamins or produce certain ones in sufficient quantities, but a balanced diet including fruit, vegetables, grains, dairy products and meats is generally all we need to cover our vitamin requirements.

Most water-soluble vitamins are found in large quantities in vegetables and fruit, with the exception of vitamin B12, which is found mainly in animal products. For this reason, people who follow a vegan diet must take care to compensate for the lack of vitamin B12 in their diet. Since 1998, folic acid (B9) has also been added to white flour, pasta and cornmeal.

As for fat-soluble vitamins, they are found in a variety of plant- and animal-based foods (see table below). In Canada, adding vitamin D to milk has been mandatory since the 1960s.

Since the body does not store water-soluble vitamins, a deficiency may become apparent after a few months. In contrast, fat-soluble vitamins and vitamin B12 are stored mainly in the liver. As a result, a deficiency may take several months or even years to become apparent.

Symptoms of deficiency are numerous and vary depending on the vitamin. The key point to remember: In developed societies, serious deficiencies are rare and occur mainly in individuals with particular nutritional and digestive problems, such as alcoholism, malnutrition, intestinal malabsorption, bariatric surgery, excessively strict diet or, in the case of vitamin D, lack of exposure to sunlight.

Here are some examples of the most common deficiencies:[1]

Vitamin D

Among other things, this vitamin is necessary for the absorption of calcium and phosphorus in the intestine. Consequently, deficiency is associated with weakness of muscles and bones. In infants, it shows up as rickets: A soft skull, slower bone growth, and a delay in sitting up and moving around. In post-menopausal women, vitamin D deficiency can make osteoporosis worse.

Vitamin B12 and folic acid

These two vitamins are essential for the production of red blood cells. Deficiency of either or both can therefore lead to anemia (fatigue, pallor, weakness, etc.), sometimes severe, with neurological damage that can persist in elderly people. Folate deficiency during pregnancy is closely associated with a higher risk of having a newborn with a congenital deformity of the spinal cord or brain at birth. In the elderly, vitamin B12 deficiency is associated with memory loss, irritability and other mood disorders, often making the diagnosis difficult to distinguish from Alzheimer’s disease and other forms of senile dementia.

Vitamin C (ascorbic acid)

Severe vitamin C deficiency is very rare in societies where the food supply is adequate. It is characterized by fatigue, weakness and irritability. Severe deficiency, once seen in sailors, is responsible for scurvy, which is also characterized by bruising and problems with gums and teeth.

Vitamin B1 (thiamine)

Thiamine plays an essential role in energy production by the cells, and a deficiency can lead to loss of appetite, intense fatigue and weight loss. In more severe cases, this deficiency is responsible for beriberi, a condition that can lead to neurological and cardiac disorders. In other cases, there may be weakness of the muscles, sometimes leading to muscular paralysis.

Vitamin A (retinol)

Vitamin A plays a crucial role in vision. Deficiency, which is very rare in developed countries, is mainly characterized by problems with the eyes, such as reduced visual acuity and dryness of the cornea, which can lead to irreversible blindness.

For the vast majority of individuals, a vitamin deficiency can be easily remedied by adjusting the diet to include a variety of meats, vegetables, fruit, grains and other vitamin-rich foods (see table). For people with special conditions, many vitamin and multivitamin supplements are available in pharmacies and natural-food stores. It is important to ensure that the products carry a DIN code for medications or an NPN code for natural products, which guarantees their approval by Health Canada.

Required doses vary from one vitamin to another and according to the medical condition. In most cases, it is easy and prudent to follow the recommended daily allowance (RDA) or adequate intake (AI) (see table). It is important to remember that this dose is in addition to what is provided through diet. For certain conditions, the advice of a healthcare professional is needed to determine the doses that are effective and least likely to cause toxic side effects.

Since vitamins A, D, E and K are stored in the body for long periods, excess levels, most often due to supplements, can be toxic. Conversely, excess amounts of water-soluble vitamins are quickly eliminated in the urine and, except in cases of serious abuse, are rarely toxic.

Medical journals regularly publish cases of poisoning by each vitamin, in particular vitamins A and D, but sometimes water-soluble vitamins such as B3 (niacin), B6 (pyridoxine) and vitamin C. One study published in 2015 in the respected New England Journal of Medicine calculated that between 2004 and 2013, nutritional supplements were directly responsible for more than 23,000 emergency room visits and 2,150 hospitalizations per year in the United States.[2]

Vitamin C and biotin (B8) can interfere with certain laboratory tests.[3] Vitamin C is an antioxidant agent which in high doses can interfere, for example, with the detection of glucose and blood in urine.

As for B8, this vitamin can interfere positively and negatively with various blood parameters, including a number of hormones (T4, T3, TSH, FSH, LH, prolactin, cortisol, etc.), depending on the analysis system being used. As not all laboratories use biotin in their reagents, it is advisable to confirm these interferences by verifying a doubtful result on another analytical platform. It is important to note that healthcare professionals are not always aware of this type of interference.

*Health Canada adds choline to this list.

** RDA/AI: Recommended dietary allowance and adequate intake

*** Adequate intake only