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 per cent quicker if you take zinc supplements.
So, what other symptoms and ailments indicate a nutritional deficiency?
Here, we reveal which vitamins and minerals your body may be lacking, and how to boost your levels.
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 Britains 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 per cent 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 its 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.