Concentration Meditation and Alertness

Namaste

This is a common misconception that meditation is a form of concentration.
Have you ever witnessed a scene of natural beauty, such as an amazing sunset, and for a moment felt one with the universe, only to lose that state as soon as your mind tried to analyze what was going on?
That experience is called a spontaneous enlightenment, the best-known of them being the "near death" experience.
That would be the easiest way to understand what enlightenment and meditation are.

Enlightenment is a state of mind where we are shading off the Ego and reunite the self, the "I" the soul, spirit or whatever you want to call it with the infinite wisdom of the universe.
Meditation then would be the process of removing the "Ego", of escaping the prison of reason.
There are many forms of meditation but at the base of every form of meditation there is one principle:
The "reason" can only process one thing at the time. If you think that you can do more than one, try to do any mental activity while counting backward from 5000 to 1 - (Automatic reflexes that do not use reasoning, like driving a stickshift car do not constitute a mental activity.)

So whether you are "focusing" on your breathing, a candle flame a chant or a mantra you are basically keeping your mind from the usual continuous chatter "rumination"common to an unenlightened state.
The reason meditations do not work is because the practitioner doesn't understand the purpose of meditation and believes that "Focusing" is the desired result.
A good meditation is the one that gives you enlightenment not focus

Does anyone know whether meditation increases alertness more than exercise, or nutrition?

In the path of purification concentration preparation chapter, the concentration practitioner must has well enough self managements, such as exercise, nutrition, friend, etc, before to make the meditation growing up.

When you cultivate samatha, you cultivate the three factors:

1. Concentration
2. Mindfulness
3. Alertness

And you establish the two aspects of (1) clarity and (2) stability which oppose (1) laxity and (2) excitement respectively. The cultivation of samatha is not merely the cultivation of the concentration mental factor.

We usually compare the mental factor of 'alertness' (or introspection) to a spy that checks the state of one's mind and what the mind is doing. At the beginning of each meditation session, it is suitable to ask oneself "Is my mind heavy or light? Is it excited or calm? Is it bright or dark? Is it sleepy or awake? and so forth" because that will enable you to cultivate alertness. Then, in the context of meditation, every time you lose your object, do not run after the object that distracted you, but identify the consciousness to which it appeared. If you lost your object of concentration because of a sound, identify "ear-consciousness", etc. This also helps you to cultivate alertness.

Cultivating samatha is helpful in that, by trying to stay with an object, your learn how your mind reacts in relation to it. However, with cultivating samatha, there is the risk of bringing attachment into meditation, clinging into your object of meditation, taking a lack of concentration as a failure. This is the reason why vipassana might be more suitable. In the context of Vipassana, you can tell yourself "Concentration is not my purpose... my purpose is to understand how and why I lose my object. So my object of concentration is just an anchor". A fully qualified samatha is a union of calm abiding and special insight. Therefore you must practice both alternately.

Ethical discipline is the root of mindfulness and alertness. When you are about to break a vow or when you just broke one, the spy of alertness knows you have erred. The vows are thus a very good way of cultivating mindfulness (keeping virtue in mind) and introspection (checking where you find yourself). Non-introspection leads you to break your vows. In 'A Necklace for Those of Clear Awareness Clearly Revealing the Modes of Minds and Mental Factors' a texts on minds and mental factors by Yeshe Gyeltsen, it says:

QUESTION: What is non-introspection? RESPONSE: A wisdom that is concomitant with afflictions and engages unknowingly in activities of body, speech, and mind. It has the function of acting as a support for infractions.