The role of micronutrients in optimizing health and preventing or treating disease has been acknowledged over the last few years. It stems partly from the increase in knowledge and understanding of the biochemical functions of these nutrients and their relation to health and disease.
As important as it is for an individual to be in energy and macronutrient balance to be healthy, it is equally essential to be in micronutrient balance. Therefore, in this article, we will discuss the physiological role of micronutrients, their food sources, micronutrient deficiencies, how they can impact bodily functions and overall health, and micronutrient supplementation in specific population groups, such as athletes.
Micronutrients are essential vitamins and minerals to sustain all normal cellular and metabolic functions. While the needed amounts of micronutrients are minimal, their impact on the body’s health is critical, and micronutrient deficiencies can have a range of adverse health impacts, causing even life-threatening conditions.
Vitamins are organic compounds that the human body cannot synthesize, except for vitamin D, which is synthesized when our skin is exposed to sunlight; niacin, produced by the amino acid tryptophan; and vitamins K and biotin, which is then synthesized by the gut microbiota. In other words, all the rest of the vitamins must be obtained from the diet. Vitamins are classified based on their solubility as fat-soluble vitamins, which are the vitamins A, D, E, and K, and water-soluble vitamins, which are the B vitamins and vitamin C.
Minerals are inorganic substances that support physiological functioning and are necessary for human life. Humans cannot synthesize them, so most come from eating plants and animals and drinking water. The human body has five significant minerals: calcium, phosphorus, potassium, sodium, and magnesium. All the remaining minerals are called trace elements: iron, chloride, cobalt, copper, zinc, chromium, manganese, molybdenum, iodine, and selenium.
Micronutrients have various functions within the body. They are involved in hundreds of biological processes, including energy storage and energy production, protein metabolism, inflammation, bone metabolism, cardiovascular function, oxygen transport, immune function, tissue repair, growth, and development. More specifically, trace elements are cofactors for enzymes involved in energy production and redox processes, meaning the production and elimination of reactive oxygen species during cellular metabolism. Moreover, many B vitamins are coenzymes in metabolic processes required to accomplish these reactions. Furthermore, minerals are transcription control factors that bind to DNA and regulate the synthesis of hormones’ receptors and other proteins. Lastly, many micronutrients, such as vitamins A, C, and E, have direct antioxidant properties. Therefore, they can potentially quench the reactive oxygen species directly, limiting the oxidative damage caused by them.
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Although micronutrients are required in small amounts, they must still be ingested through diet. As part of a mixed diet, five portions of fruits and vegetables per day generally provide sufficient quantities of all trace elements and vitamins. However, some micronutrients are primarily found in animal products, such as meat, fish, eggs, and dairy. These include zinc, iron, vitamins B3 (niacin), B12, and A. Moreover, there are micronutrients, such as zinc and iron, which, although abundant in plant foods, are less bioavailable. Specifically, phytates, fiber, and lignan, compounds found mainly in whole grains, legumes, nuts, and seeds, impair their absorption, making it more challenging to meet their daily needs by just eating such foods.
The nutritional status of a micronutrient can be characterized along a continuum from deficiency to excess. Micronutrient deficiencies are a form of undernutrition. They occur due to insufficient intake, impaired absorption, and increased requirements due to pregnancy, infection, acute illness, surgery, or inflammation. Micronutrient deficiencies should readily be detected and treated since they are an established factor in many severe health conditions, including infections, congenital disabilities, cancer, cardiovascular disease, and osteoporosis. The most common micronutrient deficiencies, which are also those of the most significant public concern, are the following: iron, vitamin A, vitamin D, iodine, folate, zinc, and vitamin B12.
A basic rule of a nutritionally adequate diet is the principle that it must contain a variety of foods from several different food groups. Therefore, food-restrictive diets or any diet that completely excludes a specific food group could be improved regarding micronutrient intake. For example, vegan and vegetarian diets that exclude all animal-based foods increase the risk of causing iron, zinc, and vitamin B deficiency, especially B12. Similarly, extreme energy-limiting diets, such as very low-calorie diets (VLCDs) or low-calorie diets (LCDs) used unsupervised by individuals who wish to lose weight quickly, cause an increased micronutrient deficiency risk. Therefore, it’s always prudent that people who want to initiate a weight loss effort or, in general, alter their dietary habits by adopting nutritional patterns that exclude whole food groups, such as the vegan diet, consult with a registered dietitian to eliminate the chances of any nutritional deficiencies.
Typically, the long-term consumption of a well-balanced diet will provide a healthy individual with adequate amounts of all the micronutrients for normal bodily functions; hence, there is no additional benefit from micronutrient supplementation in such cases. On the contrary, supplementing micronutrients at levels exceeding the Reference Nutrient Intakes (RNIs) when there is no evidence of inadequate micronutrient intake, especially for micronutrients that are stored in the body, such as the fat-soluble vitamins may be harmful. Notably, research has shown that higher doses of vitamins E and A increase all-cause mortality and lung cancer, respectively. Therefore, clinical benefit is most probable in those people who are severely depleted and at risk of complications. This is especially important to underline, given the considerable inclination, especially among individuals who go to the gym or practice sports, to supplement with micronutrients for performance purposes when there is no benefit from such a routine.
Nevertheless, professional athletes may have increased micronutrient requirements indeed. Such cases include but are not limited to, athletes with high sweat and urine losses who are at increased risk of electrolytes (sodium, potassium, magnesium) and zinc deficiency, athletes with low energy intakes, such as female gymnasts or athletes in sports with weight divisions who are at increased risk of iron deficiency (female athlete triad syndrome), vegan/vegetarian athletes who are at risk of vitamin B12 deficiency, and athletes who compete in winter sports or mostly train indoors who are at risk of vitamin D deficiency. Micronutrient supplementation for such individuals is beneficial and sometimes mandatory to support health and performance. This has been confirmed by several studies which have consistently associated micronutrient deficiencies, such as iron, calcium, magnesium, zinc, and selenium, in athletes with compromised athletic performance due to reduced aerobic capacity (VO2max), lowered lactate threshold, reduced recovery capacity, diminished strength, and reduced mood.
To sum up, micronutrient deficiencies are a significant health concern worldwide; thus, strategies for upgrading the nutritional status of populations should involve efforts to increase dietary diversity. For example, agricultural interventions, food fortification, etc. This becomes especially meaningful if we reflect on the fact that micronutrient deficiencies are mostly prevalent in developing countries of low-income populations with a lack of access to various foods. When incomes are low, people rely on inexpensive sources of calories, which tend to be poor sources of many micronutrients. Conversely, more nutrient-dense foods, such as fruits, vegetables, and animal products, are more expensive and currently beyond the reach of these populations.
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