Despite following all the healthy eating advice about getting your five a day, experts suggest many of us lack the vitamins and minerals essential for keeping us fighting fit.
Though we are advised to try to get as many of these as possible through our diet, pills may help top up our levels.
Indeed, a recent study revealed that you will recover from a cold 40 percent quicker if you take zinc supplements.
"Understanding how best to define and measure optimum nutrition will make the application of new technologies to allow each person to optimize their own nutrition a much more realistic possibility than it is today." said Joyce C. McCann, Ph.D., a co-author of the study from the Nutrition and Metabolism Center at Children's Hospital Oakland Research Institute in Oakland, California. "If the principles of the theory, as demonstrated for vitamin K and selenium, can be generalized to other vitamins and minerals, this may provide the foundation needed."
McCann and colleagues reached their conclusions by compiling and assessing several general types of scientific evidence. They tested whether selenium-dependent proteins that are essential from an evolutionary perspective are more resistant to selenium deficiency than those that are less essential. They discovered a highly sophisticated array of mechanisms at cellular and tissue levels that, when selenium is limited, protect essential selenium-dependent proteins at the expense of those that are nonessential. They also found that mutations in selenium-dependent proteins that are lost on modest selenium deficiency result in characteristics shared by age-related diseases including cancer, heart disease, and loss of immune or brain function. Results should inform attempts to locate mechanistic linkages between vitamin or mineral deficiencies and age-related diseases by focusing attention on the vitamin and mineral-dependent proteins that are nonessential from an evolutionary perspective.
OTHER SYMPTOMS: Poor concentration, poor appetite, pale skin, dark circles under the eyes.
RECOMMENDED DAILY ALLOWANCE (RDA): 14.8mg for women and 8.7mg for men.
WHAT IT DOES: Needed to make red blood cells. A component of haemoglobin, which transports oxygen round the body.
WHO NEEDS IT: Iron deficiency is Britain’s most common nutritional disorder, according to studies presented recently at the National Conference on Iron Deficiency in Infancy and Childhood.
It affects up to 18 percent of women due to blood loss through menstruation.
Others who may be deficient include people who suffer minor bleeding in the intestines, such as those with a peptic ulcer or who take aspirin.
GOOD SOURCES: Red meat, eggs, green leafy vegetables. Vitamin C helps the absorption of iron, so it’s a good idea to drink a glass of orange juice with a meat-based meal.
OTHER SYMPTOMS: Poor wound healing, white marks on nails.
RDA: 7mg for women and 9.5mg for men.
What it does: Helps make new cells and enzymes and is essential for wound healing. It has also been linked to healthy sperm production.
WHO NEEDS IT: The World Health Organisation estimates a third of the global population is zinc-deficient.
In Britain, this may include children and teenagers with a poor diet, pregnant women and elderly people.
Vegetarians should also be aware that cereals containing chemicals called phytates block absorption when eating zinc-rich food. Iron supplements also hinder zinc absorption.
GOOD SOURCES: Nuts, seeds, wholegrains, crab, sardines and red meat. You can get a daily dose of zinc from a single oyster or a 200g piece of beef steak.
DEFICIENCY: Riboflavin (Vitamin B12).
OTHER SYMPTOMS: Dryness and cracking of skin around the mouth and nose.
RDA: 1.1mg for women and 1.3mg for men.
WHAT IT DOES: Keeps skin, eyes and nervous system healthy.
WHO NEEDS IT: One in ten adults is said to have low Vitamin B12 intake.
GOOD SOURCES: Milk, eggs, rice, fortified breakfast cereals. A large glass of semi-skimmed milk (around 300ml) gives you just under half the RDA of Vitamin B12, as does 150g of grilled lean rump steak.
BACK & LEG PAIN
DEFICIENCY: Vitamin D.
OTHER SYMPTOMS: Hip pain, brittle bones.
RDA: 10mcg (men and women).
WHAT IT DOES: Bone growth and helping the absorption of calcium in the gut. It is also important for a healthy immune system.
WHO NEEDS IT: Everyone, but particularly older women and young children. A recent survey showed more than half of the adult population has insufficient levels of Vitamin D.
GOOD SOURCES: Dietary sources are poor; the most readily available source is sunlight on the skin. Twenty to 30 minutes on your face and forearms three times a week should provide enough of a store for the winter.
OTHER SYMPTOMS: Frequent bouts of ill health.
RDA: 75mcg for men and 60mcg for women.
WHAT IT DOES: It boosts immunity, protects cells from damage and may help fight cancer: a study of 42,000 people in Europe is looking at its effect on cancer risk.
Selenium may also be important to a man’s fertility — a study by the University of Padua in Italy and published in the journal Science found that a diet low in selenium could affect the quality of a man’s sperm.
WHO NEEDS IT: We should all consider improving our intake, says dietician Dr Sarah Schenker.
GOOD SOURCES: All your daily needs are in seven brazil nuts.
OTHER SYMPTOMS: Out-of-character irritability.
RDA: 300mg a day for men and 270mg a day for women.
WHAT IT DOES: Helps convert food we eat to energy, and ensures the health of the para-thyroid glands in the neck, which produce hormones important for bone health.
Essential for maintenance of bones and teeth, which use 60 percent of our body’s total magnesium content.
This metallic element is also vital for the transmission of nerve impulses, the contraction of muscles and the regulation of body temperature.
WHO NEEDS IT: Premenstrual women and the elderly, who need magnesium to maintain healthy bones.
GOOD SOURCES: Spinach — 90g gives almost three-quarters of our recommended daily allowance. Also found in almonds and wholemeal bread (one slice equals 10 percent of RDA).
DEFICIENCY: Vitamin A.
OTHER SYMPTOMS: Frequent colds and infections, flaky skin, dandruff.
RDA: 0.7mg a day for men and 0.6mg a day for women.
WHAT IT DOES: Helps fight infections, boosts vision in dim light and keeps skin healthy.
WHO NEEDS IT: Severe deficiency is rare, but low intakes are relatively common in adults, says Dr Elizabeth Weichselbaum, of the British Nutrition Foundation.
But pregnant women are advised not to take supplements containing Vitamin A or eat liver (which is high in the nutrient) because it has been linked to an increased risk of birth defects.
According to research, having more than an average 1.5mg a day of vitamin A over many years may affect your bones, making them more likely to fracture when you are older.
GOOD SOURCES: Liver, eggs, cheese and yogurt.