Russell Blaylock MD, neurosurgeon, nutrition research expert, has devoted 8 pages of the June, 2011 edition of his newsletter to the topic:  Magnesium.
Magnesium is considered the most forgotten and the most important miracle mineral. It is critical for every tissue in the body and is involved in over 300 enzymatic processes necessary to sustain life.  I'll just list a few so that you can get a greater appreciation for this energy spark-plug.
Magnesium can:
1.  relax blood vessels  (it will stop spasms)
2.  stop inflammation (from virus infection, industrial pollution, toxic metals, pesticides and herbicides, excess iron, oxidized fats, high levels of excitotoxins - eg: MSG, aspartame, etc.)
3.  protect cells from the inflammation-triggering effect of calcium  (our bodies need calcium, too, but not at the levels recommended by most physicians.  If you take any form of calcium, it should be balanced by magnesium in a 2:1 ratio (favoring magnesium)
Deficiencies in magnesium are linked to many health issues:
1. heart disease
2. strokes
3. atherosclerosis
4. abnormal kidney function
4. muscle weakness
5. diabetes
6. insulin resistance
7. metabolic syndrome
8. inflammation
9. excitotoxicity (caused by aspartame, MSG, soy protein isolate, all "fake meat" products based on soy, etc)
10. neurodegenerative diseases (alzheimers, parkinsons)
11. impaired lung function
12. cancer
13. immune system disorders
14. depression and even suicide 
All chronic diseases take a long time to develop.  They are the result of years and years of tissue inflammation, many times undetected.  (a good reason to have your C-reactive protein levels and homocysteine checked every year).
As your body becomes more inflamed with age, your risk for developing inflammation-related diseases increases.  Hypertension, heart disease, cancer, neurodegenerative disease and strokes are all the result of years of untamed inflammation.
Some antidotes for inflammation: 
1.  a plant based diet - the more fruits and vegetables in your diet, the less inflammation you will have.  (one of the most recent studies on JuicePlus+ showed a significant reduction in several blood inflammation markers - this is a big deal) 
2.  moderate but not heavy exercise  Moderate exercise opens up anti-inflammatory channels in the arteries.  Heavy exercise does the opposite and causes much oxidative damage (read: inflammation). 
3.  Relaxation -   learning how to do deep-belly breathing a few times each day (see website article - click website below), run, play, walk in the sand, unwind, listen to a relaxation CD. 
4.  Be/stay in love - being involved in loving relationships lengthen telomeres (honestly!) and lengthen life.
5.  Take magnesium!   Dr Blaylock recommends 500 - 1000 mg a day of only certain forms of magnesium, like magnesium citrate and magesium malate and magnesium glycinate, half in the a.m and half in the p.m.  These forms  absorb the best.  Magnesium oxide is very poorly absorbed. 
Those who use JuicePlus+ can get by on a lot less but I still recommend JP+ users add 200 - 400 mg of magnesium every day.  If your bowels can't tolerate very much magnesium you might look into the magnesium oil that you can rub on your skin.  (internet search:  magnesium oil)
There!  I just saved you 8 pages of fine print!!