A Guide to Micronutrients: Functions, Recommended Intakes and Food Sources

Protein, carbohydrate and fat get almost all the attention in a gym. Yet the reactions that turn those macronutrients into usable energy do not run without vitamins and minerals. This guide looks at what happens when micronutrient intake is chronically low, what the main vitamins and minerals actually do, which ones people most often fall short on, how much is recommended, and where the evidence on multivitamins currently stands.

A quick look at metabolism

Metabolism is a word coaches and members use constantly, usually without a clear picture behind it. It is simply the sum of the countless reactions running continuously to keep a body alive with little or no conscious effort: breathing, thinking, a heartbeat, digestion, circulation, movement.

Keeping all of that running takes two things: nutrients and oxygen.

The six classes of essential nutrients

Six classes of nutrients are essential to human health, meaning we cannot go without them without negative consequences. The body does not make them, so they have to come from the diet:

• carbohydrate;
• protein;
• fat;
• vitamins;
• minerals;
• water.

Carbohydrate, protein and fat are known collectively as macronutrients because they are needed in large amounts. They supply calories, that is energy in the form of ATP, to drive every metabolic reaction. Those reactions are triggered by proteins called enzymes, and enzymes need cofactors in order to work. That is where vitamins and minerals, the micronutrients, come in. They are needed in far smaller quantities, but the machinery stops without them.

What selected micronutrients actually do

• B vitamins are required to extract energy from food.
• Vitamin C is a powerful antioxidant and plays an essential role in maintaining a strong immune system.
• Vitamin B12 is required for normal nerve function and for making red blood cells.
• Vitamin A is required for vision, immunity and healthy skin.
• Vitamin D is required for bone formation and healthy immune function, and acts as a hormone throughout the body.
• Vitamin E is an antioxidant and helps protect cells from damage.
• Vitamin K is required for blood clotting and for directing calcium to bone.
• Calcium is required for muscle contraction and bone formation.
• Iron is required to transport oxygen around the body.
• Magnesium regulates muscle contraction and nerve transmission, contributes to the formation of teeth and bone, and is required for more than 300 metabolic reactions.
• Potassium is required for muscle contraction, proper nerve conduction and the maintenance of fluid and electrolyte balance.

There are roughly 30 vitamins and minerals that have to be consumed regularly. Many have multiple functions and work synergistically to run the metabolism that keeps a person alive and healthy.

How much do you actually need?

Scientists at the Institute of Medicine established the daily amounts of each micronutrient to consume, known as RDAs, or recommended dietary allowances, broken down by age, sex and life stage. It is important to understand what those values are for: they are set to prevent deficiency and the diseases and conditions that come with it. They are not necessarily the amounts that are optimal for longevity.

The practical dietetic advice that follows from this is unglamorous and hard to improve on: eat a wide variety of colourful, minimally processed foods from all the major food groups. That maximises nutrient intake while staying within the calorie needs that maintain or move towards a healthy weight.

What a micronutrient-dense diet looks like at 2,200 calories a day

• 3 cups of vegetables a day, split across the week as:
  • 2 cups a week of dark green vegetables (spinach, which is also a good iron source);
  • 6 cups a week of red and orange vegetables;
  • 2 cups a week of legumes (beans and peas);
  • 6 cups a week of starchy vegetables (potatoes, green peas, corn, plantains);
  • 5 cups a week of other vegetables (iceberg lettuce, mushrooms, onions, cabbage).
• 2 cups of fruit a day.
• 3.5 ounces of whole grains (wholemeal bread, brown rice, oats, quinoa).
• 3.5 ounces of other enriched refined grains (white rice, refined cereals, pasta).
• 3 cups of dairy.
• 6 ounces of protein foods, split across the week as:
  • 9 ounces a week of seafood;
  • 28 ounces a week of meat, poultry and eggs;
  • 5 ounces a week of nuts, seeds and soya.
• 29 grams of oils.

Written out like that, the pattern looks demanding but achievable. The survey data says otherwise.

The nutrients people most often fall short on

In the United States and other developed countries, frank deficiencies and the classic deficiency diseases are rare. Inadequate intakes, below the recommended allowance, are not. The 2015-2020 Dietary Guidelines for Americans report identified nine widely under-consumed nutrients:

• calcium;
• magnesium;
• potassium;
• vitamin D;
• vitamin A;
• vitamin C;
• vitamin E;
• choline;
• fibre.

The reason becomes obvious once you look at where the calories are coming from. The six largest sources of calories in the American diet identified by the Dietary Guidelines Committee were, in order: grain-based desserts (cakes, biscuits, doughnuts and similar), bread, chicken and mixed chicken dishes, soft drinks, pizza, and alcoholic drinks.

It is safe to say that most people eating that way are not eating a micronutrient-dense diet. With pizza at number five, sodium intake is a fairly safe bet too. These figures are American; comparable national surveys in Europe are run under different methodologies, so the specific shortfall list should not be transposed country by country without checking the local data.

What happens when intake stays low

Because vitamins and minerals are needed for so many physiological processes, chronic shortfalls affect many aspects of health and metabolism at once. There is evidence linking micronutrient insufficiency to several age-related chronic diseases, including cancer, osteoporosis and heart disease (McCann and Ames, 2011; Ames, 2018).

The mechanism proposed for this is worth understanding, because it explains why nothing appears to be wrong for years. When a micronutrient is in short supply, the body rations it: the functions needed for immediate survival are served first, and the functions that protect long-term health are served last, or not at all. Vitamin K is the standard illustration. The clotting proteins get their share before the proteins that keep calcium out of arteries and in bone. Nothing hurts, nothing shows up, and the cost is paid decades later in what we call the diseases of ageing.

Folate and the birth of the prenatal vitamin

Folate, vitamin B9, occurs naturally in legumes and leafy vegetables. It is required for DNA synthesis and supports cell growth and repair. Low folate status is linked to neural tube defects, and there is evidence for a role in stroke prevention (McNulty, Pentieva, Hoey, Strain and Ward, 2012).

Folate as it occurs in food is less stable and less well absorbed than folic acid, the synthetic form, which is considerably more effective at building up stores. Multivitamin and mineral formulas containing folic acid have been shown to reduce neural tube defects, and a prenatal vitamin is now a global recommendation during pregnancy and for women of childbearing age (Czeizel and Dudas, 1992).

In 1998, folic acid was added to the American food supply through the fortification of refined grain products, and the prevalence of newborns with neural tube defects fell. Whether or not anyone thought of it that way, populations have been supplementing for decades.

Calcium and the bone-building micronutrients

Most Americans do not meet their daily requirements for the nutrients involved in building bone, namely calcium, magnesium, vitamin K and vitamin D, for reasons that range from food preferences to access. Around 99 per cent of the body’s calcium is stored in the skeleton. The remaining fraction circulating in the blood is held within a very narrow range, because essential functions depend on it.

When calcium intake is insufficient, the body breaks down bone to hold that blood level steady and keep the heart beating. Over time, chronic shortfalls of calcium and the nutrients that work with it produce weakened bone and osteoporosis. You survive in the short term at the expense of long-term health, and because the damage is invisible and painless, most people do not know there is a problem until it is too late.

Where a multivitamin fits

Most adults carry health insurance, dental insurance, car insurance, contents or mortgage insurance, life insurance, sometimes pet insurance. All of it exists to cover an outcome that may never happen. Very few carry the nutritional equivalent.

A low-dose multivitamin and mineral covering a broad range of under-consumed micronutrients, matched to age, sex, life stage and activity level, does exactly that job: it covers vitamin and mineral needs on the days food does not (Blumberg, Cena and Barr, 2018). As the survey data shows, most people do not get everything they need from food alone.

A well-formulated multivitamin is emphatically not a replacement for a complete diet. It supplements food intake so that the micronutrient floor is met.

Supplements worth considering when the diet is short

Where intake of specific food groups is low, the supplements worth considering are calcium, iron, vitamin D and omega-3 fish oils. These bring intakes up to recommended levels and act as nutritional insurance.

Survey data consistently shows that supplement users have fewer micronutrient inadequacies and higher micronutrient intakes. Compared with food alone, multivitamin and mineral use was associated with a lower prevalence of inadequacy for 15 of the 17 micronutrients examined. Multivitamin and mineral supplements have also been shown to substantially reduce the prevalence of inadequate intakes of calcium, magnesium and vitamins A, C, D and E. Similar findings have been published in other countries.

Why this belongs in a facility operator’s thinking

For a gym, box, hotel spa or rehabilitation centre, none of this is a licence to sell nutrition advice. It is a reason to be precise about scope. Members who train hard on a low-micronutrient diet plateau, recover badly and get injured, and they will blame the programme or the equipment before they blame their diet. Knowing where the boundary sits between coaching and dietetics, and having a referral route to a registered dietitian, protects both the member and the business.

It also affects how a floor is planned. Recovery and regeneration have moved from an afterthought to a revenue line, and a well-specified wellness and recovery area gives members a reason to stay in the building rather than leave straight after their session. The same logic applies to the cardio equipment mix: variety keeps people training consistently, and consistency is what makes any nutritional effort worth making.

Frequently asked questions

Are RDAs optimal amounts?

No. RDAs are set to prevent deficiency and the conditions associated with it. They are a floor, not an optimum for long-term health or longevity.

Can a varied diet cover micronutrient needs without supplements?

In principle yes, and that remains the goal. In practice, national survey data repeatedly shows that most people do not achieve it, which is the argument for low-dose nutritional insurance rather than for replacing food.

Which micronutrients are most often short in an active population?

Calcium, magnesium, potassium, vitamin D, vitamin A, vitamin C, vitamin E, choline and fibre are the nutrients identified as widely under-consumed. Athletes on restricted or weight-loss diets are at greater risk, because cutting whole food groups cuts micronutrients with them.

Should a gym give nutritional advice?

General education about food groups and variety is one thing; individual dietary prescription is regulated and belongs to qualified professionals. Refer, and keep the two clearly separate.

Summary

The human body is built for survival and has sophisticated mechanisms for coping with chronic micronutrient shortages, rationing what is available towards the proteins and functions that keep you alive today while sacrificing the vitamin- and mineral-dependent proteins that protect long-term health. Meeting the recommended daily amounts of roughly 30 micronutrients is therefore every bit as important as hitting your daily macros.

Maximising micronutrient intake means eating varied food sources from all the major food groups consistently. Dieting for weight loss, avoiding whole food groups, or eating the same narrow set of foods all restrict micronutrient intake and lead to larger vitamin and mineral shortfalls. Low-dose multivitamin and mineral use has been shown to help bring intakes up to the recommended amounts that support physiological function today and long-term health tomorrow.

References

1. National Academies of Sciences, Engineering, and Medicine. (2019). Dietary Reference Intakes for Sodium and Potassium. The National Academies Press. DOI 10.17226/25353
2. Ames BN. Prolonging healthy aging: longevity vitamins and proteins. Proceedings of the National Academy of Sciences, October 2018, 115 (43) 10836-10844. DOI 10.1073/pnas.1809045115
3. McCann JC, Ames BN. Vitamin K, an example for triage theory: is micronutrient inadequacy linked to diseases of aging? Am J Clin Nutr. 2009;90(4):889-907. DOI 10.3945/ajcn.2009.27930. PMID 19692494
4. McCann JC, Ames BN. Adaptive dysfunction of selenoproteins from the perspective of the triage theory. FASEB J. 2011;25(6):1793-1814. DOI 10.1096/fj.11-180885. PMID 21402715
5. McNulty H, Pentieva K, Hoey L, Strain J, Ward M. Nutrition throughout life: folate. Int J Vitam Nutr Res. 2012;82(5):348-354. DOI 10.1024/0300-9831/a000130. PMID 23798054
6. Czeizel AE, Dudas I. Prevention of the first occurrence of neural-tube defects by periconceptional vitamin supplementation. N Engl J Med. 1992;327(26):1832-1835. DOI 10.1056/NEJM199212243272602. PMID 1307234
7. Blumberg JB, Cena H, Barr SI et al. The use of multivitamin/multimineral supplements: a modified Delphi consensus panel report. Clin Ther. 2018;40(4):640-657. DOI 10.1016/j.clinthera.2018.02.014. PMID 29573851
8. Blumberg JB, Frei BB, Fulgoni VL, Weaver CM, Zeisel SH. Impact of frequency of multivitamin/multimineral supplement intake on nutritional adequacy and nutrient deficiencies in US adults. Nutrients. 2017;9(8):849. DOI 10.3390/nu9080849. PMID 28792457
9. Wallace TC, McBurney M, Fulgoni VL 3rd. Multivitamin/mineral supplement contribution to micronutrient intakes in the United States, 2007-2010. J Am Coll Nutr. 2014;33(2):94-102. DOI 10.1080/07315724.2013.846806. PMID 24724766