Health and Longevity is a concern of all. We not only want to live a long life, we want to live a healthy one. One major reason why people get annual Astrology readings is to check for potential health problems for the upcoming year. Jyotish is extremely accurate in predicting the onset of illness and making recommendations to help lessen or subvert the illness entirely.
Our physical body is an expression of our mind and spirit. When we make better choices in our mind we have a healthier body. When our Spirit is light and content our mind is better able to make better choices. The Birth Chart is a representation of the Spiritual, Mental and Physical bodies. Difficult houses in the Chart or the problem planets that rule them show where and what type of illness will manifest in the body.

Looking for WeaknessMedical Astrology is very tricky. First the inherent strength of the planets must be measured through all of the ShadVargas. (Vimshopaka) Planets with a low Vimshopaka score are especially problematic and show a weakness in that dhatu. (Ayurvedic building block) Then debilitated planets or ones in dusthana houses or under malefic aspect are found. This will show which  element is weak. It is the weakest Planet(s) that will be the culprit of disease. Their Sign / House and the dasa periods will signal the onset of that illness in that location.      
Varga Charts
Vedic Astrology uses many Harmonic charts (called Vargas) to fine tune all areas of life. The main chart used in medical Astrology is the Rasi or Birth chart as it shows the body and overall constitution. But also of major importance is the Trimsamsha (d-30) chart as it shows the overall susceptibility to illness and general physical strength. The Drekkana (d-3) is also important as it shows the vital energy and ability to fight disease. And also the Dwadasamsha (d-12) will show the inherited genetic factors that contribute to our overall health. A confluence of factors in these charts will show what and where serious illness may occur and how to prevent it.
Preventative Strategies
In Medical Astrology there are 5 elements just as in Ayurveda and  each planet rules one of the 7 dhatus.

To prevent disease weak planets are helped using Ayurvedic principles which balance the 3 doshas, the 3 properties of our imbalanced nature. Through diet, mantra, aromatherapy, etc we can heal ourselves before we become ill. Once ill or sick, recovery is greatly enhanced using these remedies.

Element:
Earth - Mercury, spleen, stomach
Air - Saturn, large intestine
Water - Venus, kidney, urinary
Ether - Jupiter, liver, gall bladder
Fire - Mars, heart, small intestine

Dhatu:
Sun - bone - minerals - mineral absorption
Moon - blood - water - overall body tissue
Mars - marrow - electrolyte (dissolved minerals) energy
Mercury - skin - surrounding tissue - cell walls
Jupiter - fat reserve
Saturn - nerves - channel of the life force
Venus - semen - hormones - endocrine system