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What and when you eat and drink can be important in helping to keep you alert, focused and able to deal with the day-to-day pressure of exams.

It is an old rule but a golden one: during periods of intensive study, breakfast really isvital. Numerous studies have indicated that skipping it affects the ability to concentrate later: those who eat breakfast have better recall, better problem-solving skills and improved scores in maths tests.

The explanation for this is probably that your brain has high glucose requirements yet can store only small amounts of this crucial source of energy.

It was always assumed that the body kept the brain optimally supplied with glucose (sugar) at the expense of almost every other organ. But this idea is challenged by the finding that boosting blood sugar after a night¡¯s fast aids mental performance.

The precise mechanisms by which blood sugar affects memory are not fully understood, but glucose is certainly needed to raise production of a nerve transmitter called acetylcholine. When drugs block production of acetylcholine, memory is disrupted, with the ability to remember new information being particularly affected.

While a sugary breakfast cereal and white toast, or a pain au chocolat or muffin will certainly give you a sugar rush, it is less likely to keep your blood sugar stable for the morning ahead than the slowly digested carbohydrates that are found in, for example, wholegrain cereals such as porridge and sugar-free muesli, granary toast or some fruit with a yoghurt or fromage frais.

Wholegrain cereals also give you a dose of B vitamins, including the B1 that is needed, along with blood sugar, to make acetylcholine. Meanwhile, the milk that you add to your muesli provides protein, which helps to keep you full and aids concentration.

For mid-morning snacks try to avoid quickly digested, refined carbohydrates such as biscuits, cereal bars, fizzy drinks and squash or sweets. A sugar burst followed by a debilitating, energy-draining low can result, which is enough to throw your concentration off kilter in exams or make revision more difficult.

It is also vital to keep well hydrated. Even a small dip in fluid levels can affect our ability to focus and may impair mental agility. During revision, it is better to make frequent trips to the loo than to sit and stare blankly because, deprived of fluids, you can¡¯t absorb information properly. During the exam it is a good idea to keep taking small sips of liquid, provided you have been to the loo before you begin.

While coffee, tea and energy drinks such as Red Bull might seem to help in staving off sleepiness during late-night revision sessions, overdoing these beverages can overstimulate the nervous system, elevating blood pressure and heart rate and putting you more ¡°on edge¡±. Stick to no more than five or six caffeine-containing drinks each day.

To get the most out of caffine¡¯s short-term ability to improve concentration, it is worth cutting down your daily intake and saving such a drink until just before you really need the boost.

Lunch is as important as breakfast. The last thing you want, however, is the feeling that a rich meal is sitting uncomfortably in your stomach all afternoon. Avoiding fat-laden, mayonnaise-based sandwiches, pizzas and chips is therefore wise.

So, too, is steering clear of meals that are too rich in carbohydrate. Large pasta-based dishes and oversized baguettes will deliver a big dollop of carbohydrate, which can make you sleepy in the hours ahead so that you feel more like a siesta than hard mental work.

Protein, on the other hand, seems to help us to concentrate. Tuna, chicken, turkey, lean beef or ham and eggs make ideal bases for lunch and can be accompanied by slowly digested carbohydrates such as a small pitta bread, tortilla wrap or a slice of rye, sourdough or granary bread.

It is also worth considering taking a multivitamin and mineral supplement such as MultiBionta or Centrum to help to give you an insurance policy for vitamins and minerals. For instance, too little iron has been shown to reduce people¡¯s ability to concentrate, and can possibly trigger low moods ¨C the last thing you need at exam time. Surveys of British teenagers show that girls, particularly, are lacking in iron, consuming only about half the recommended daily intake between the ages of 11 and 18.

A general lack of B vitamins can strain the nervous system, while too little folic acid (a specific type of vitamin B) can, like insufficient iron, trigger low moods.

Quick tips for smart candidates

¨C¨C Boost your omega3s. Omega3 essential fats are vital for optimum brain functioning, helping messages to reach nerve endings effectively. Two servings a week of oily fish such as salmon, mackerel or anchovies, plus regular intakes of flax seeds and omega-3-enriched eggs, orange juice and milk are worth eating.

¨C¨C Avoid junk food, cakes, biscuits, pies and ready meals that contain trans fats (labelled as ¡°partially hydrogenated oils/ vegetable fats¡±) in the ingredients list. It is believed that these can block the passage of messages between nerve endings in our brains.

¨C¨C Have plenty of citrus fruits, berries and vegetables, which are great for vitamin C. Our adrenal glands, which pump out adrenalin when we are stressed, need good supplies to keep our bodies in balance. As vitamin C is needed for a robust immune system as well, these fruits and vegetables may also help to reduce the risk of being laid low with a summer cold that could upset your revision and exam performance.

¨C¨C Replace some of your caffeine-rich, sugary drinks with camomile tea: the active plant constituents can help to reduce stress.