Health and longevity are two related concepts.
Death occurs when a vital organ fails, so having a good general health improves longevity.
Also living a long live with a lot of pain (bad health) makes no sense.
There are two approaches about this problem:
Improving lifespan in mice
Recently (15 December 2016) some researchers at Salk Institute managed to increase lifespan for mice suffering progeria disease without changing the progeria gene.
In Vivo Amelioration of Age-Associated Hallmarks by Partial Reprogramming
They induced cells to return to pluripotent state during a sort space of time, so cells autorepair themselves.
Until this one, experiments trying this path had resulted in mice developing a lot of tumors.
Anyway this approach is still very experimental and not applicable to humans.
Opposite approach
Because we do not know how to increase our lifespan, we try the opposite approach, that is avoiding death.
Most common causes of death in developed countries:
http://www.who.int/mediacentre/factsheets/fs310.pdf
https://en.wikipedia.org/wiki/List_of_causes_of_death_by_rate
THE TEN LEADING CAUSES OF DEATH IN HIGH-INCOME COUNTRIES 2002
| Cause | % of deaths |
|---|---|
| Coronary heart disease | 17.1 |
| Stroke and other cerebrovascular diseases | 9.8 |
| Trachea, bronchus, lung cancers | 5.8 |
| Lower respiratory infections | 4.3 |
| Chronic obstructive pulmonary disease | 3.9 |
| Colon and rectal cancers | 3.3 |
| Alzheimer and other dementias | 2.7 |
| Diabetes mellitus | 2.7 |
| Breast cancer | 1.9 |
| Stomach cancer | 1.8 |
Deaths in millions from WHO in 2001:
| Cause | Millions of deaths |
|---|---|
| Ischaemic heart disease | 3,512,000 |
| Cerebrovascular disease | 3,346,000 |
| Chronic obstructive pulmonary disease | 1,829,000 |
| Lower respiratory infections | 1,180,000 |
| Lung cancer | 938,000 |
| Car crash | 669,000 |
| Stomach cancer | 657,000 |
| Hypertensive heart disease | 635,000 |
| Tuberculosis | 571,000 |
| Suicide | 499,000 |
We observe preventing heart and cerebro-vascular disease would diminish the 17.1 + 9.8 = 26.9% of deaths.
So main conclusion is take care of your cardiovascular system!