Our immunity, physical strength, ability to fight diseases, endurance, prana energy can be known by significance, strength of Sun (Surya) and Ascendant (Lagna).
Sun is the tanu (self or body) kaaraka in any horoscope.
Sun is the life force as it lends vitality, energy and life to native. A well placed Sun in the horoscope is indicative of a body that is strong and robust.
Weak of malefic Sun indicates weak and disease prone body which is prone to frequent ailments.
Sun is fiery planet with a Agni tatva, representing energy and vitality. Generally, if Sun and Ascendant lord are not well placed, that person cannot handle physical pain and struggle to recover from a disease.
Generally, athletes, body builders, sports persons, physically fit people have a benefic and strong Sun in their birth chart.
Sun placed in 6,8,12 houses can make a person have weak body.
Along with Sun, planets signifying and aspecting Lagna also help boost immunity or act otherwise.
3 Agni Tatva (fire) signs are strongest of all
People born under ascendants (Lagna) of Aries (Mesha), Leo (Simha) and Sagittarius (Dhanu) are considered strongest and can recover from ailments faster than others.
This is proved right especially if they have Sun placed in benefic houses and in friendly signs of Aries, Cancer, Leo, Scorpio, Sagittarius and Pisces.
Sun in Libra (Thula) is at its weakest point (generally born during 16 october – 15 november of every year) and these people if abuse their body, can get sick quicker.
After Agni Tatva signs, 3 Earth Signs Taurus (Vrishabha), Virgo (Kanya) and Capricorn (Makara) are stronger and can recover from illness faster than others.
They have robust built and disciplined lifestyle. This helps them to stay away from ailments as long as possible.
But if at all get infected, with some disciplined diet and medication, they can fight back to normal health soon.
After Bhu Tatva (earth) signs, 3 Airy Signs Gemini (Mithuna), Libra (Thula) and Aquarius (Kumbha) lagnas can do better while recovering from illness.
However, they can effected by wind related ailments such as asthma, flu, viral infections. Also blood pressure, migraines are possible.
If sick, they can recover only with medication and rest.
Staying away from airconditioners, polluted atmosphere and infected people can save them to large extent.
After Vayu Tatva (Airy) signs, people born under 3 Jala Tatva (Watery) ascendants Cancer (Karkataka), Scorpio (Vrischika) and Pisces (Meena) are the least robust.
They can suffer easily from cold, cough, phlegm related diseases and viral infections.
Out of these 3 signs, Scorpio ascendant born can do better as they have natural fighting ability and are capable of regular physical workouts.
Among the nakshatras, those born with Moon at 4th quarter of Mercury owned nakshatras (Aslesha, Jyeshta, Revati) and 1st quarter of Ketu owned nakshatras (Aswini, Magha, Moola) are with most weakest physical strength.
Moon controls mind and plays an important role in recovery.
Those born with a weak moon (closer to Amavasya or New Moon day) can get sick due to their worrisome attitude.
Also their recovery will be slow due to their pessimistic thinking.