Indeed one very simple but surprisingly accurate assessment of your own health is to take a close look at the health of those around you and, in particular, your partner's.

Recent medical research has established that how healthy or unhealthy one person in a marriage or long term relationship is, is strongly associated with the fitness of the spouse. There is also an accumulation of findings that illness seems to cluster in families, neighbourhoods, communities and social groupings. So basically the health of your relatives, neighbours and friends is probably a strong predictor of yours.

Dr Julia Hippisley-Cox and colleagues of Nottingham University recently published an investigation of 8,000 married couples in the British Medical Journal which found that couples are up to 70 per cent more likely to suffer from the same kind of disorders. For example the risk of high blood pressure goes up by 32 per cent if your wife or husband has it, while the likelihood of raised levels of harmful blood fats - called hyperlipidaemia - goes up by 44 per cent.

The findings suggest that in future doctors will perhaps automatically screen a partner if they find certain illnesses in the spouse, the link between ill health being shared in a marriage is so strong. The theory to explain these extraordinary results is, as the conditions being studied were not infectious, that married couples may copy each others habits - so if one shuns healthy eating and hates going to the doctor, then the other may as well.

Dr Sven Wilson of Brigham Young University in the USA concludes his own recent investigation of how families differ significantly in health with the startling statement that: "Sick people are not randomly distributed across the population, they tend to be married to other sick people."

But it is also the case that just having a relationship, as opposed to being alone, seems to be good for your health. A substantial amount of medical research now agrees that being married significantly improves your longevity over being single, divorced or separated. For reasons that aren't entirely clear Dr Wilson found that the statistics indicate that the mortality risk for men dramatically drops from the day they get married - in other words getting hitched is good for the health of men immediately. But for women, although they benefit as well, it seems their mortality risk improves slowly with each year of marriage.

Male health appears to gain from marriage by a change to a more "settled" lifestyle (fewer late night kebabs, alcoholic binges and less sleeping around) while female health seems to gain predominantly through access to increased financial resources - in comparison to those who don't marry.

However exactly why being married helps you live longer remains unclear but new research from Joan Tucker and psychologist colleagues of Brandeis University in the USA, which for the first time probed in depth couples relationship history, suggests a key issue is the state of health of the relationship itself.

This study found that even if you were currently married, but had been divorced in the past, this significantly shortened your life span. It seems that the transition in the past from being married to divorce, even if you later remarried had a profoundly negative impact on fitness. Perhaps the stress of the break up, even though you were now in a settled relationship, had had long term effects on health. This would suggest that stressful relationships in themselves are perhaps worse for our well-being than we had previously realised.

Supporting the idea that it's the quality of relationships within a family that determines your health, a recently published study of German families from the last two centuries found there is a kernel of truth to all those mother-in-law jokes after all.

The research by Dr Eckart Voland and Dr Jan Beise of Giessen University in Germany found that an intrusive paternal mother-in-law had a significantly negative impact on the health of grandchildren in a family. This was in contrast to an intrusive maternal mother who seemed to lead to significantly reduced chances of early childhood mortality. The findings remain deeply puzzling. But one tentative theory, which relies on some huge generalisations, is that perhaps the maternal mother tends to provide support to mum so enhancing her ability to provide high quality child care. In contrast possibly an interfering paternal mother-in-law tends to be critical of the mother, and so reduces her confidence and functioning capability.

Just how potent an influence on health conflict within a family could be is illustrated by another recent study published by Dr Gregory Miller and other psychologists from the University of California. They measured how the immune, hormonal and cardiovascular systems in 41 married men changed during just a 15 minute discussion of a marital problem. They found significant differences in the way blood pressure was elevated and how active protective white blood cells became depending on the health of these men's relationships. These profound biological changes occurred when the men were encouraged to discuss a marital problem with a neutral investigator in the laboratory - therefore one could only shudder to think what is happening to the body in the middle of a marital row!

That even the community where you reside could influence your health was recently established by research conducted by Dr Gerry Veenstra, an anthropologist at the University of British Columbia, who examined the health of neighbourhoods in Canada. He found a strong link between the "social capital" of a community and its health. Social capital is a new buzz term amongst sociologists and is a way of thinking about the fact that, while they might differ in material wealth, communities can be compared on social resources. Social capital is an attempt to measure social cohesion, trust and willingness to engage in community activities: basically how well your neighbours get on with each other and are willing to be put out for each other. The more your neighbours care for you in general the better your health tends to be.

That who you know and how things are going between you and others can determine your health, and even how long you live, might seem surprising at first glance but in fact the first consultation about your health is not usually with a doctor - its with someone you know well. A discussion with your partner, or relatives, or friends - where they eventually admonish you to go to a physician or take time off for sick leave - usually provides the necessary reassurance to finally make an appointment. Sometimes it even takes an observant friend to point out that you are actually not as well as usual, or that you are exhibiting a symptom.

If you are surrounded by those who don't take regular exercise, eat a healthy diet or bother much with seeing doctors, no matter how ominous the symptom, then it could be this "health culture" influences your own health more than you realise. It is obviously going to be much more difficult to stay healthy if practically everyone you know drinks to excess and encourages you to share their aversion to fresh vegetables.

How healthy the food is that is available in your local store is probably hugely influenced by the demand for such products amongst those who live around you - as is the availability of gyms, tennis courts or other features of a healthy lifestyle.

Indeed this new way of thinking about health begins to explain some previously puzzling data. For example it was always mysterious as to the precise reason why Alcoholics Anonymous and other similar substance abuse self-help groups are such a powerful mechanism for help with various addictions. It now seems that one surprisingly simple answer is that by religiously going to such abstinence groups, you gradually give up your old drinking and drug abusing buddies who led you astray, and replace them with new abstemious friends you meet at these groups. These new relationships help you model and live a healthier lifestyle. If it was bad friends who were going to eventually kill you, then it's new healthier acquaintances that are going to save your life.

This new orientation in medical science is actually a quiet revolution. It means that when evaluating health and predicting longevity doctors are now not just looking at the individual patient any more, but now need to take into account who they know, who they are married to and what kind of neighbourhood they live in.

This means the patient should probably begin to do this as well and that if they want to improve their own well-being they might have to help their partners, friends and relatives improve their health as well.

The research has established that negative interactions within relationships, such as conflict and criticism, are associated with worse health - but also that their impact on well being is greater than that of supportive relationships.

This suggests that besides giving up smoking, excessive drinking and an unhealthy diet, you should also consider cutting down on those relationships that could be damaging your health.