Food is the fuel for life. It provides us with energy for movement, brain activity and growth. But food is much more than just calories – it has the power to dramatically affect our health, both causing and curing disease. Obesity and Type 2 Diabetes are diseases of the diet, whereas eating whilst observing rules of good nutrition can prevent many cancers, osteoporosis and promote optimal function of the immune system and brain. The importance of the diet in maintaining and promoting health goes far beyond the macronutrients protein, fat and carbohydrate. Hidden in abundance in all foods is a vast array of micronutrients each as essential to life as food itself. These micronutrients are described by the world health organisation as “magic wands”; they are responsible for all aspects of bodily functions from muscle contraction to gene regulation and are vital for normal growth and development to occur throughout life. Micronutrients include vitamins, minerals and trace elements. They are only required in very small amounts and both an absence and excess can have a considerable impact on health.
Part 1: Vitamins
In part one of this micronutrient series I will focus on a select few vitamins essential for maintaining energy levels and optimal immune function, along with their other vital health-enhancing roles in the body: what goes wrong if too much or not enough is present in the body along with current recommended intakes and the best food sources for meeting the body’s needs.
Vitamin A is a fat-soluble vitamin. Compounds with vitamin A activity, including retinol and beta carotene, play a key role in vision, regulation of gene expression and cell differentiation, particularly of immune cells. The carotenes also act as antioxidants mopping up harmful free radicals.
Vitamin A is involved in the ability to adapt to changes in light, allowing us to see in the dark and detect colours. Low vitamin A status will initially impact on the ability to detect green light, with increasing deficiency leading to poor adaptation to dim light and eventually xerophthalmia – a condition of irreversible damage to the cornea of the eye which results in blindness.
Vitamin A’s role in immune cell differentiation means a low intake can reduce the ability to fight off infection.
Foods containing high levels of vitamin A compounds include eggs, dairy products, liver, leafy green vegetables like spinach and broccoli and yellow or orange vegetables such as carrots, squash and sweet potatoes.
The body converts all sources of vitamin A into retinol and so when considering which foods to choose for their vitamin A content, we need to look at the retinol equivalent activity. In males and females over 14 years, the recommended intake is 700 and 900 micrograms of retinol activity equivalent, respectively. Getting exactly the right amount of vitamin A each day would involve eating half a cup of carrots and a quarter of a cup of cooked spinach, half a sweet potato, or 0.3 oz of beef liver. The good news is that vitamin A is fairly abundant if the diet includes a broad range of animal proteins and vegetables. Also, being a fat-soluble vitamin, it can be stored within body fat, which means that it doesn’t need to be consumed at the recommended amount every day.
Although adults are capable of eating up to ten times the recommended intakes each day without seeing negative effects, the liver has a limited capacity for metabolising vitamin A. Toxicity is observed when people routinely consume more than 8 milligrams per day of retinol compounds. Signs of vitamin A accumulation in the tissues include headaches, nausea, joint pains, dry scaly skin and hair loss. Over-consumption of carotenes is not associated with toxicity but some studies have linked it with an increased risk of lung cancer mortality in men . Vitamin A toxicity is very difficult to achieve from diet alone and since there are so many delicious food sources of both retinol and carotene, it should not be difficult to obtain sufficient vitamin A without recourse to supplementation.
The B vitamins are a group of vitamins vitally important for energy production, nervous system function and the synthesis of components in the blood. The following B vitamins are of key importance:
- B1 (thiamine)
- B2 (riboflavin)
Vitamin B1,also known as thiamine, is essential for carbohydrate metabolism, energy production and plays a role in nerve impulse conduction. Acting as a coenzyme (a molecule that aids the activity of an enzyme) for three enzyme complexes
involved in energy-generating pathways, thiamine helps facilitate a series of chemical reactions that result in energy release. Thiamine deficiency is associated with very heavy alcohol intake; poor diet – highly processed food and refined carbohydrates or insufficient intake of food; persistent vomiting. Conditions caused by thiamine deficiency are severe and affect function of the brain and limbs. Unless you fall into the above categories you are unlikely to suffer any thiamine related issues but maintaining adequate intake is still important. Daily requirements depend on the amount of carbohydrate eaten and should be at least 0.8mg per day for women and 1mg for men. People eating a highly refined carbohydrate diet need and should consider including more thiamine in their diet. Good sources of Vitamin B1 include: pork, vegetables, milk, eggs and wholegrain bread. Vitamin B1 cannot be stored and so must be eaten every day. It is not necessary to supplement as daily requirements can be met by the diet alone.
Vitamin B2(riboflavin) also acts as a coenzyme working to aid metabolic processes crucial for unlocking the energy stored in macronutrients. Deficiency can be due to poor diet or an inability to
absorb dietary sources. The overall result of deficiency is a reduced ability to metabolise fats, which stunts growth and prevents normal development. Signs and symptoms may include badly cracked lips and a dry, painful mouth and tongue, dry skin and bloodshot eyes, but deficiency is rarely fatal. The main sources of vitamin B2 are dairy products, although eggs, nuts, leafy green vegetables and lean meats provide good alternative sources. Adults should aim to eat about 1.5mg every day, as it is a water-soluble vitamin and so unable to be stored in the body. It is sensitive to light, so foods should be kept in dark containers and eaten soon after cooking. Mushrooms, spinach and almonds are particularly tasty, excellent sources of B2. Mushroom and spinach omelette, anyone?
Vitamin B6 unsurprisingly perhaps, plays its role in energy metabolism but is also important in the synthesis of haemoglobin, the component of blood that binds and transports oxygen around the body. Both of these roles are fundamental for maintaining optimal energy levels. It also acts on DNA to help regulate the release of steroid hormones, as well as being important for cognitive development. Deficiency is uncommon and most people are able to meet their daily needs through diet alone. Good sources of vitamin B6 include: beef, poultry and fish, along with many of the vegetables that provide the other B vitamins. Toxicity due to over-consumption from foods is not known to be a problem, but can be observed in those taking supplements long-term . Loss of feeling in the limbs can be a sign that Vitamin B6 levels have become toxic, as well as skin lesions and gastrointestinal problems, including nausea. In most cases, symptoms will cease once supplementation is stopped. Adults should aim to eat more than 1.2mg per day from wholefood sources. Supplementary vitamin B6 might be necessary for people with renal dysfunction, autoimmune disease and alcohol dependence.
Vitamin B12 another water-soluble vitamin, is ingested bound to protein in our food. It is released by the digestion process in the stomach and used as a coenzyme for a number of reactions involved in the synthesis of haemoglobin, DNA, hormones and the metabolism of fat and protein. Deficiency can cause weakness, fatigue, loss of appetite, constipation and eventually megaloblastic anaemia. Low vitamin status without full deficiency can have a number of neurological implications, including: numbness of the hands and feet, balance loss, confusion and memory loss and in the advanced stages depression and dementia. Daily intakes of 2.4micrograms are considered adequate for everyone over 14 years, with animal products, particularly fish and beef, being the highest dietary sources. Fortified breakfast cereals (though watch the sugar levels!) and dairy products are good alternatives for vegetarians and fussy eaters. Vitamin B12 levels are thought to be adequate in most of the population but certain groups are at risk of poor status. Older people and anyone with digestive or intestinal complications may have a reduced capacity for absorbing this essential nutrient. Vegetarians may not ingest enough high vitamin sources unless eating fortified cereals daily, along with dairy products. For these ‘at risk’ groups, supplementation may be an option if dietary intake cannot be modified to meet individual needs.
We are all familiar with the immune-boosting qualities of a good dose of vitamin C, but perhaps more impressive when it comes to the immune system and antioxidant super powers, is vitamin E.
Vitamin E’s health enhancing qualities extend far and wide within the body. It acts as a powerful antioxidant, preventing free radicals generated by fat metabolism, as well as combatting the effects of external sources of oxidative damage. Free radicals are reactive oxygen molecules that, if left to roam free, can cause considerable damage to all cells. Vitamin E also appears to play a strong role in reducing cardiovascular disease, as vitamin E-saturated cells lining blood vessel walls are less susceptible to damage and vascular constriction, both prognostic markers of cardiovascular disease. Vitamin E deficiency in humans is mostly unlikely, although certain groups with poor fat absorption, as in cystic fibrosis and chronic liver disease, will be at high risk, as vitamin E is fat-soluble.
Recommended intakes relate to alpha-tocopherol, as this is the only form that has a significant biological activity in humans. 15mg of alpha-tocopherol equivalent intake per day is considered adequate for everyone aged 14 and over. Nuts, seeds and olive oil, along with cooked spinach and broccoli, are just some of the healthy foods that contain good levels of natural vitamin E. Synthetic vitamin E only provides half the amount of active alpha-tocopherol compared to natural whole food sources and so twice as much needs to be consumed. Due to vitamin E’s role in prevention of blood clotting (as an anticoagulant, it inhibits blood platelets from clotting abnormally) and potential to increase oxidative stress, over-consumption can lead to adverse health effects including haemorrhage and increased prostate cancer risk . This is unlikely to be an issue unless taking very high dose vitamin E supplements.
Given the amazing super powers of these vitamins, it is tempting to think that you should get as much as possible into the body to maximise your health potential. This is definitely a great thing to consider when it comes to choosing what to eat, as this will ensure a varied and high nutrient diet that will leave you feeling energised, mentally sound and physically fit.When it comes to non-dietary sources of vitamins, i.e. supplements, these should never be the first consideration when it comes to maximising vitamin intake. Many supplements contain low grade, inactive ingredients and often contain lots of chemicals and potentially harmful substances. As in the case of vitamin E, over-consumption of vitamin supplements can lead to severe toxicity and serious health implications. Most people are able to meet their daily nutrient requirements by eating fresh vegetables and a range of fruits along with a variety of animal protein and natural foods. If you are worried about your nutrient intake, always aim to improve through diet first. If you are still concerned about deficiency or low nutrient status, talk to your GP or nutritionist who may wish to investigate further.
Why, then, if vitamin supplements are largely unnecessary and can, in unnecessary doses, be harmful, do so many people take them? People often believe that taking a vitamin supplement is a simple and effective option to top up levels and gain additional benefits. Vitamins themselves require additional factors in the diet to help unlock their powers; taking a supplement may not provide these essential dietary particles and so the body may be unable to utilise the extra dose of vitamins. This will be discussed further in parts two and three of this micronutrient article series, where minerals and trace elements are considered. Even with optimal minerals and trace elements present in the diet, the body only has a limited capacity to metabolise and utilise vitamins; anything above and beyond daily requirements can build up or get wasted.
Interested to know more about supplements in general? Keep an eye out for the upcoming article: Supplements: what should I be taking? This article will address the current evidence for taking a range of supplements, from multivitamins to fish oils and amino acids.
 The Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study Group. The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. N Engl J Med 1994;330:1029-35.
 Bendich A, Cohen M. Vitamin B6 safety issues. Ann N Y Acad Sci 1990;585:321-30. [PubMed abstract]
 Klein EA, Thompson Jr. IM, Tangen CM, Crowley JJ, Lucia MS, Goodman PJ, et al. Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA 2011;306:1549-1556. [PubMed abstract]
D.A. Bender “Micronutrients – Vitamins and minerals”. Introduction to Nutrition and metabolism. 4th ed. CRC press. Chapter 11. p317-381.
Sophie Tully has joined Igennus as Nutrition Technical Advisor. Passionate about health and fitness, she decided to build on her pharmacology and cancer research background and undertake an MSc in clinical nutrition. Sophie is now determined to show people that ‘optimal health’ is not just being disease-free. It is about living a long and happy life without reliance on medication, or suffering ongoing illness. ‘Health’ results from a delicate balance of nutrition, physical fitness and mental wellbeing, specific to each of us. Each aspect is equally important and reliant on the other two – one element alone can shift the balance and impact on health.