Friday, 24 February 2017

The origins of life - rock and water

And now for something completely different....

This is very different from my usual Blog Posts, but I hope you will find the subject as fascinating as I have found it.

The inorganic origins of organic life

Moonset over London - a long way from the origin of life


The “Big Bang” story of the start of the Universe 14 billion years ago is rather dull: there was nothing and then in less than a microsecond later there was everything. The Book of Genesis is much more interesting; it says the same thing but with a longer time-scale. There are countless other similar and imaginative creation stories composed by the many groups of people in the world.  

Creation – The Ancient of Days. William Blake

After or during creation, “everything” had be be remodelled into things that we can see and things that we cannot see – matter and anti-matter, visible energy and dark energy.

The Earth itself appears to have been created 4.5 billion years ago, and a lot has happened since then. 

The evolution of the Universe during 14 billion years


The Just So Stories” (Rudyard Kipling 1865–1936) have given colourful suggestions of the evolutionary origins of some advanced animal species, but these would have been in comparatively recent years. The great mystery is how and where life itself originated. 

Eukaryotes (cells with nuclei), the cellular building blocks of the advanced forms of life, appeared about 1.6 billion years ago. Before this, there were just bacteria and archaeadiscovered only recently. 

But life had its very earliest origins 4.5 billion years ago. 


There is a suggestion of panspermia, the seeding of life from comets into a receptive Earth environment, bringing the fundamentals of life from great distances. 

The concept of panspermia  has its origins in the 5th century BC writings of the Greek philosopher Anaxagoras, with further suggestions in the 19th century. Fred Hoyle (1915–2001) and Chandra Wickramasinghe (born 1939) have proposed panspermia in modern times. 

Hoyle and Wickramasinghe have suggested that recent pandemics of “flu” might have been due to viral DNA or RNA seeded from comets. This is an interesting but untestable hypothesis.

An acceptance of panspermia only begs the question of the mechanism of the origins of life elsewhere. It also acknowledges that evolution still had to take place on Earth: man and other advanced animal life could hardly have arrived by cometary transport.

Although panspermia cannot be excluded totally, it is perhaps more likely that life on Earth originated on Earth.


Zircons are usually tiny mineral deposits less than a millimetre in diameter, but there are lager examples that can be fashioned into attractive jewellery. The important thing about zircons is that they can be dated back to times shortly after the creation of the Earth.

The chemical composition of zircons is basically zirconium silicate, ZrSiO4. However zircons contain several impurities, which give the gem-stones a variety of colours. 

One of the major impurities is uranium. This is of course radioactive and it decays to lead. The more recently the zircon was formed, the higher the ratio of uranium to lead. But in practice the ratio of lead is high, indicating a very ancient time for the formation of zircons. They can be dated to the very origins of the Earth.

The detailed analysis of zircons indicates that at the time of their formation, more than 4 billion years ago, the atmosphere contained water vapour, nitrogen and carbon dioxide. There was between 100 and 1000 time as much carbon dioxide as at present, as there was of course no plant life to absorb carbon dioxide and to release oxygen. Oxygen is a highly reactive element and all oxygen was in the form of oxides of carbon, hydrogen, and many metals. There was ample liquid water, indicating that temperatures were similar to what they are today.

There have been many major cataclysms disrupting the surface of the Earth and its atmosphere, but the sea bed remained much more stable.

The chemical constituents of life

The formation of life had to start off with the components that were already present 4.5 billion years ago. 

Life is fundamentally composed of carbon, hydrogen, oxygen and nitrogen. These are available as combinations in the forms of water (H2O), carbon dioxide (CO2), methane (CH4) and nitrogen. 

Nitrogen is found as a gaseous atomic dimer (N2), which is free in the atmosphere. Oxides of nitrogen (NO, NO2, N2O) are gaseous but form solid compounds as nitrates and nitrites.

The other important simple compound is hydrogen sulphide (H2S), which is a gas at a temperature of the freezing point of water. Water (H2O) is unique as a simple low molecular weight compound, being in liquid form at ambient temperatures (20–40 degrees Celsius). At normal atmospheric pressure it becomes a gas at the relatively high temperature of 100o Celcius.

Carbon, hydrogen and oxygen will form fats and carbohydrates (sugars). Nitrogen is necessary in addition to form amino acids, the basis of proteins and nucleic acids (RNA, DNA).

Cysteine, a simple amino acid, made up of hydrogen, oxygen, sulphur, nitrogen

All these constituents were readily available 4 billion years ago, as they are today. It is likely that they have been available on other planets. But more than just the atomic building blocks of life were necessary for life to begin.

Polymers and the development of organic compounds

Two other things were necessary for simple organic molecules to be created, and for them to be assembled into complex molecules. 

Life is composed of simple sugars, fats, amino acids and nucleotides, but these must be polymerised, built up into long chains. 

Pentane, a 5-carbon polymer of methane
Polymers of glucose form starch as an energy store in plants, glycogen as a similar energy store in animals, and cellulose, a structural polymer in plants. Various long-chain fats  are polymers of methane. Complex proteins are polymers of amino acids. DNA and RNA are polymers of nucleotides.

The need for sustained energy

For the synthesis of simple and then complex organic molecules, a source of constant energy was necessary. 

There has been the suggestion that life started from an atmospheric chemical “soup” with the energy input being from flashes of lightning. However lightning does not provide the constant and manageable energy flow that would have been necessary. The surface of the Earth would not have been sufficiently stable for life to develop, and zircon analysis indicates that the atmosphere would not have been suitable.

The source of constant energy has been found in structures deep in the oceans.

Deep sea alkaline vents

Lost City, 60 metres tall

It is now thought that life started in deep sea alkaline vents. These are not the superheated hot smokers that we are more aware of, but rather less dramatic structures that have been discovered more recently. Water at moderate temperatures emerges from deep sea alkaline vents into rock structures with heights up 60 meters. The most famous of these structures is known as “Lost City”. 

The important features are that the water emerging is not very hot, is alkaline, and contains dissolved hydrogen and methane. 4 billion years ago the sea was much more acid than today, as the result of much more carbon dioxide in the atmosphere.

Lost City and similar alkaline vents are high towers of a sponge-like arrangement of the mineral olivine (Magnesium Iron Silicate). Olivine is hydrated into serpentine, a common mineral that polishes well and has been used in many buildings, such as the Empire State Building. 

Alkaline water with pH 9–11 percolated through a sponge-like matrix, with at the time acid sea water  with pH 5–7 on the other side of the porous rock plates that make up the “sponge”, rock as thin as one micrometer. This separation of acid and alkaline created an electro-chemical gradient, not unlike a battery, with a difference of proton concentration 1,000 to 100,000-fold. This was the constant source of energy that was necessary for the creation of organic molecules and ultimately life. This was the environment in which "protocells" (the forerunners of free-living cells) developed within the pores of the thin rock plates of the sponge matrix.

Catalysts and enzymes

The second necessity to enable a chemical reaction to take place is a catalyst, something that accelerates a chemical reaction but is not consumed by it. This is provided in the alkaline vents by the many metals that are found within the rock, in particular iron. Many other metals such as nickel and copper also act as catalysts. Think also of platinum in the catalytic convertor of a car exhaust system. 

Tiny metal clusters became incorporated into the rock and in particular into the walls of the pores in the rock. They were thus in a strategic position to catalyse chemical processes.

As organic life developed the iron (and other metal) atoms became incorporated into highly complex protein enzymes, enzymes being biological (organic) catalysts. They are still within us today, the metal atoms from the very beginnings of life. An example is the iron atoms at the core of the complex protein haemoglobin, which carries oxygen within our blood.

The complex proteins that make up enzymes are concerned mainly with the flow of negatively charged electrons and positive charged protons (nuclei of hydrogen atoms). This is fundamental to the control of electro-chemical energy within living organisms.
Serpentine (polished)

Although magnesium and iron are the most common metals to be found in the important olivine and serpentine rock, nickel, aluminium, zinc and manganese can also be found in the silicates that make up the serpentine family of minerals. They all add to the range of catalysts, becoming essential trace-elements incorporated into the complex enzymes that were synthesised throughout the evolution of a wide range of life forms. It was the Dutchman Albert Kluyver (1888–1956) who demonstrated that similar biochemical processes are present from “bacteria to elephants”.


LUCA was the Last Universal Common Ancestor of all life today, the great and unlikely accident in the development of the Earth.

The important steps in the early evolution of life

LUCA  was formed within the serpentine based sponge-like rock of the alkaline vents. It was not free living, but it was an entity that had become metabolically active. Its later developments were along two distinct and very long pathways, the bacteria and archaea. Their antecedents could only be released from the rock once they had developed protective cell walls. They also required metabolically active energy systems to replace the energy supply that sustained LUCA in the alkaline vents. In addition they required the more complex enzymes and genetic control proteins. These developments occurred during the course of half a billion years.

The development of cells

Cell walls were developed from droplets of oil, a relatively simple process involving the polymerisation of methane and also its hydroxylation to glycerol. 

The cells later absorbed what were initially free-living entities and these added much to the cell function. They included: ribosomes, for protein synthesis; mitochondria, for energy production; cyanobacteria, to enable photosynthesis in plants; spirochaetes, to form flagella that enable motility.


Mitochondria transformed cellular life through a huge increase in energy production. Without mitochondria complex life could not have developed.


Mitochondria were initially free-living bacteria that developed membranes that enabled the production of large amounts of energy. This was through the Krebs cycle of energy from the oxidation of glucose the energy being stored as ATP (adenosine tri-phosphate, a simple organic compound), with water and carbon dioxide as waste products. 

The next stage was endosymbiosis, mitochondria becoming incorporated within cells for mutual benefit. A cell can contain up to 40,000 mitochondria, which reproduce to enable cell division without mitochondrial loss. The complex protein enzymes of mitochondria include atoms of iron from the earliest origins of life. Imagine 4 billion years after the creation of life, 40,000 mitochondria in each of 10 trillion cells in our body.

To give an idea of the power of mitochondria. I quote from Nick Lane (see below):

“A single cell consumes around 10 million molecules of ATP every second! The number is breathtaking. There are about 40 trillion cells in the human body, giving a total turnover of ATP of around 60–100 kilograms per day – roughly our own body weight. In fact, we contain only about 60 grams of ATP, so we know that every molecule of ATP is recharged once or twice a minute.”

"There is an electrochemical potential difference across the membrane, in the order of 150 to 200 millivolts. Because the membrane is very thin (around 6 nm thick) this charge is extremely intense across a short distance.... the field strength is 30 million volts per metre, equal to a bolt of lightning, or a thousand times the capacity of normal household wiring."

Nick Lane

The importance of simple inorganic gases

Interesting new research has investigated the role of mitochondrial “down-regulation” in mammalian hibernation, with a shut-down of energy and heat production. There is great curiosity concerning what can restore (switch on) normal mitochondrial function, and this is relevant to human illness in which there might be mitochondrial down-regulation. Studies of hibernating mammals suggest that hydrogen sulphide (H2S) might be responsible for inducing hibernation and for reactivating mitochondria. 

Other functions of hydrogen sulphide are also suspected. This is relevant to the origin of life four billion years ago as hydrogen sulphide is a simple gas, common and present undersea geothermal vents, especially in the “smoking chimneys”. However today it appears that hydrogen sulphide is produced in the body from the sulphur-contianing amino acid cysteine.

Incidentally, I before retirement I had great interest and considerable experience in patients with chronic fatigue syndromes (CFS, ME, SEID). I came to understand that the basis of the illness was a physiological down-regulation of mitochondria during an acute illness, but failure of restoration of normal mitochondrial function when the acute illness (usually infection) had settled. I had no curative treatment to offer, but the recognition of the importance of hydrogen sulphide might well provide a therapeutic opportunity in the future.

Nitric oxide (NO) is another simple gas with early origins that has important physiological actions today. One is the control of blood pressure and other cardiovascular effects. Nitric oxide is produced in the body by the action of sunlight on nitrates from the diet, as the blood circulates through the skin. This is one reason why the sun has effects greater than can be observed from vitamin D supplements.


But these are different stories. The important message from this Post is to draw attention to how life was originally formed from the interaction of water and rock.

Our complex biology is based on simple inorganic origins that remain of great importance today.

The ages of the Earth


The writing of this Post would not have been possible without the information contained in the remarkable book "The Vital Question", by Nick Lane, Reader in Evolutionary Biochemistry, University College London. 

I recommend it to those with a deeper interest in the subject of the inorganic origin of life.

Saturday, 28 January 2017

Belfast, Toulouse, and the Sun

Belfast, Toulouse, and the Sun
Titanic Museum, Belfast

Previous Blog Posts have identified the epidemic of coronary heart disease (CHD) in the UK and also in the USA. Strictly speaking it has been a pandemic, as it occurred simultaneously in all continents, just the tropics having been spared.

The onset of the pandemic in the UK was in the mid-1920s, recorded in a similar way  in all continents. It was described in the UK very clearly and in great detail by Dr Maurice Campbell. His work was published in the British Medical Journal in 1966. At that time the death rate from CHD was still increasing, but it was very close to the peak, and the CHD death rate had just started to fall in the USA. 

The onset of CHD appears to have provoked no curiosity. But in the USA the spontaneous and dramatic fall in the death was very puzzling and people started to think about the reason for it. As a result a Bethesda Conference was convened, to bring together those with the most interest and knowledge. The conference led to the MONICA project (multinational monitoring of trends and determinants in cardiovascular disease).

Although the strict objective was to explain the sudden  reduction of CHD deaths, the identification of its cause was obviously included. The “cause” remained far from clear, and what followed was an industry of “risk factor identification”, reaching a total of 246 by 1981. These gave false messages to the population as most seemed to create a sensationalist headline in the newspapers. This continues today as risk factors tend to be confused with cause, which is elusive.

Variation and susceptibility 

The problem has been the failure to separate “cause” from “susceptibility”. One specific disease will have one specific cause, and this will be international. The incidence of a disease will vary depending on a variety of factors that will influence susceptibility. These can be within communities, families, and nations.

One example is cigarette smoking. It is one of the most clearly defined risk factors for death from CHD. A detailed study of UK doctors showed that 20% of heavy smokers died from CHD, but so did 20% of non-smokers. So where is the risk? The long-term study showed that by 50 years of age, twice as many heavy smokers had died from CHD compared to non-smokers. Also, death from CHD occurs on average ten years earlier in heavy smokers compared to non-smokers. Cigarette smoking cannot be regarded as the cause of CHD, but it is an important risk factor. Furthermore it is a risk factor that can be modified, unlike others such as baldness (to my knowledge the effect of the wearing of wigs by bald men has not been investigated).


Geography appears to have a major impact on the susceptibility to death from CHD. In the UK there is a gradient of deaths rate from CHD, highest in the north-west and lowest in the south-east. To try to identify an explanation, the Three English Towns Study (which we have seen in a previous Post) failed to do so. There was no significant variation of smoking incidence or dietary pattern. It is generally assumed that the answer lies in differing but unknown behavioural patterns of the regional populations. In other words the victims are assumed to be to blame.

Map of the UK showing mortality rates by region

Location of residence also becomes obvious when looking at the variation of death rates from CHD within Europe: death rates are low in southern Mediterranean countries, and high in northern European countries. The reason is not clear. Greece has the highest prevalence of cigarette smoking but the lowest risk of death from CHD. 

We have seen that the very influential Seven Countries Study pointed at dietary cholesterol as the explanation of variation of CHD deaths. However the conclusion pre-dated the study, which itself was very seriously flawed and is now discounted. Diet does not explain the wide variation.

The explanation of the variation of CHD mortality remains far from clear, but the MONICA study has provided a powerful process of investigation.


Belfast: Harland & Wolff shipyard, where the Titanic was built

Rather than investigate large populations in many countries superficially, one off-shoot of the MONICA project was to investigate two smaller populations in great detail. The populations of Belfast, in Northern Ireland, and Toulouse, in the South of France, were chosen. Two papers were published. The first was part of the MONICA project itself, and this studied 366 people in Belfast and 400 in Toulouse. Detailed dietary assessments were based on 80 and 40 people.

The south of France, close to Toulouse

The PRIME study (prospective epidemiological study of myocardial infarction) was established later to investigate the serious problem of excessive premature death of men in Belfast. The lead investigator for PRIME was Alun Evans, professor of epidemiology and public health at Queen’s University, Belfast, Northern Ireland. He and his team undertook a detailed comparison between many population characteristics of the cities of Belfast and Toulouse, in the south of France.

Many epidemiological studies have looked at national statistics, and national death rates in particular. These are readily available but there can be error that is not under the control of the investigator who uses the data. The PRIME study generated its own data, very detailed, collected personally, and with minimal error. The study investigated much larger population samples, 2748 men in Belfast and 2610 in Toulouse.

The Mountains of Mourne, close to Belfast
The first part of the study was to collect health data, in particular death rates from various causes, in the cities of Belfast and Toulouse. Men were studied as the greatest health concern was the apparent early death of men in Belfast. The age groups studied were 45–54 and 55–64, as death within these age groups is considered to be premature. Men dying in these age-groups had contributed to their pensions but did not receive them.

Vineyards close to Toulouse

The second part was to collect data on various risk factors that are generally thought to cause or lead to premature death, such as cigarette smoking, high blood pressure, diabetes, and high cholesterol (it is only in men of these ages that a high blood level of cholesterol gives an increased risk of CHD death, according to the major Framingham study).

The third part was to look at diet, as many people believe that diet is crucial in the cause of CHD. The popular (but seriously incorrect) diet–cholesterol–heart hypothesis is all about diet. The diet study was very detailed and the data was based in individual questionnaires.

Death in Belfast and Toulouse

The differences found were quite remarkable.

Figure 1: Death rates per 100,000 men aged 45–54 years

Figure 2: Death rates per 100,000 men aged 55–64 years

Men in these age-groups living in Belfast were much more likely to die than those living in Toulouse, 40% more likely in 45–54 age group and 85% more likely in the 55–64 age group (all causes of death). This would obviously give a very great concern for those responsible for the health of the population of Belfast.

Looking more specifically, the risk of such men in Belfast dying from CHD was more than four times more likely (>400%) than those in Toulouse. There was a 20% increase in Belfast men dying from cancer.

It was also reported that the myocardial infarction (MI) rates in men aged 35–64 was 781 in Belfast compared to 240 in Toulouse, a three-fold increase in Belfast. 

It is clear that it is much safer to live in Toulouse than in Belfast.

Risk factor analysis

The results of this part of the study are very interesting but are what might be regarded as negative.

Figure 3: Risk factor analysis, men aged 45–54 years

Figure 4: Risk factor analysis, men aged 55–64 years

Firstly, the prevalence of diabetes was higher in the men in Toulouse, nearly three times as great in the older age-group (this could in part be case-finding or definition rather than true incidence). Hypertension and cigarette smoking rates were also higher in Toulouse. The BMI and cholesterol levels were very similar. 

It can be seen in Figures 3 and 4 that the overall prediction of risk of death from CHD was effectively identical for the men in Belfast and Toulouse. This is very different from the reality shown in Figures 1 and 2, indicating the lack of value of risk factor profiles.

There is at present health tendency to predict survival and CHD risk of individuals on the basis of “risk-factor analysis”, undertaken uncritically. It has caused unnecessary concern to several of my friends, and no doubt to countless other people. 

A good friend of mine received a telephone call from her family doctor informing her that she had “a fifty per cent chance of dying”. This came as a shock to her and it certainly created anxiety. However it could be interpreted as good news – that she had a corresponding fifty per cent chance of immortality (assuming that immortality is good news, and this is extremely doubtful). It was the sort of news that came from an over-simplified algorithm rather than from the thought processes of a normal and well-informed human brain.

It is quite clear that classical risk factors do not explain the much higher death rates of the men in Belfast compared to those in Toulouse. It must be emphasised that we are looking at risk of overall deaths, and also specific causes including CHD, stroke and cancer.


As what we eat is generally thought to be so important in the causation of CHD and other diseases, it became a major part of the MONICA and PRIME investigations. However, in the search for an answer to the high death rates in Belfast, the diet study can only be regarded as a considerable disappointment: diet did not provide the answer.

Figure 5: Dietary characteristics of men in Belfast and Toulouse 

There was a marginally higher total calorie consumption in Belfast, 2340 versus 2295 kcal per day, just 2% higher than Toulouse. There was more protein consumed in Toulouse, less fat, but the major difference was a much more cholesterol in the diet in Toulouse, 50% more than in Belfast.

There was no obvious dietary explanation for the high death rates in Belfast. The population sample in Toulouse consumed more tomatoes, but it would be stretching the imagination for this to be considered of such major health importance.


The purpose of the investigations was to try to explain: “the several-fold differences in risk of coronary heart disease between France and Northern Ireland.”

The result was that: “Neither the classic risk factor scores nor the similarity in major nutrient intake adequately explain the large differences in IHD (ischaemic/coronary heart disease) and other causes of mortality between the centres.” 

And that: “The levels of the classical risk factors found in this study….cannot explain the large differences in the incidence of IHD (CHD) which exist.”

So this exercise was effectively a failure. The studies failed to identify the “cause” of CHD, and they also failed to identify a significant risk indicator. However they clearly identified our ignorance, and this is of vital importance if scientific progress is to be made.

The studies were certainly successful if the purpose was to challenge and then demolish the popular but seriously flawed diet–cholesterol–heart hypothesis. They certainly did that. But, as with so many researchers, the authors stopped short of expressing such a statement. Unfortunately these very important papers, and the important detailed risk factor analysis, were completely ineffective in explaining the causation of CHD and regional death rates. 

In failing to draw attention to these obvious conclusions, the studies were a waste of money. They possible entailed the employment in the two cities of forty people for a period of five years. If the average salary at todays prices would be £50,000 per annum, then the total cost would have been £10 million. The studies have probably been forgotten.

The leaders of the study should have been told by their sponsors to go back and find the answer. In the late 20th century it should not have been acceptable for an 80% excess death rate of men aged 55–64 years in Belfast compared to Toulouse to remain unexplained. We are not living in the dark ages, in which the will of God would have been an acceptable explanation.

How could it be that the search for the answer came to a halt? What a failure of imagination and scientific curiosity. 


It is clear that living in Belfast is more dangerous than living in Toulouse. Of course Belfast had a period of very serious civil disorder during the years 1969 and 1994. Of a population of 1.5 million, there were 2755 deaths resulting from terrorism, the majority below the age of 40 (a further 691 deaths in people from outside Northern Ireland). Although this was tragic (and in retrospect incomprehensible), the studies described have looked at deaths not from trauma but from CHD and cancer.

The locations of Belfast and Toulouse

The only obvious difference between Belfast and Toulouse is that they are in different places. Belfast lies at 54o 60' north of the equator and Toulouse at 42o 60'. Belfast is thus is about 800 miles (1300 km) north of Toulouse. Both are important industrial cities, Belfast being where the Titanic was built, and Toulouse is the main base of the Airbus construction.

Most simply, geography appears to be of fundamental importance, and the geographical difference is latitude. How does latitude affect the population? The answer is sunlight exposure. 

The further away from the equator is the place of residence, the less is the incident sunlight per year – that is the lower the sunlight intensity or energy at ground level. 

Belfast is at a further disadvantage as it is so close to the North Atlantic Ocean and the depressions that are carried from it by the prevailing winds that follow the Gulf Stream. Belfast has a great deal of cloud cover, and consequently relatively few hours of sunshine as well and low sunlight intensity.

Within the UK we can see that the regions with the lowest death rates (in south-east England) are those that receive the most sunlight. Correspondingly, the West of Scotland has the highest death rates and the least sunshine. 

UK sun exposure map (hours of sun-shine)
It appears to be likely that the higher susceptibility of the population of Belfast to CHD is lack of sun exposure. The main, but not the only, biological effect of the sun on the body is synthesis of Vitamin D. This is known to be important in the development of immunity, and we have seen that immunity is important in protection against CHD. Not only does a reduced level of immunity increase susceptibility to CHD, but increasing immunity is likely to be the reason for the end of the epidemic.

But we can take things a stage further. We have demonstrated in Belfast an increased susceptibility not just to CHD but also to stroke, cancer, and all-cause mortality. It would appear that the sun is of great importance to human health, probably mediated via an increased level of immunity.

Final thoughts

I have communicated with Professor Alun Evans in Belfast concerning this proposal. He was fairly receptive and he told me that at the end of the investigation, those concerned wondered if climate and in particular the sun might have been the critical factor that was being sought but which had not been found. He told me that by then it was too late to include blood levels of vitamin D in the study (blood levels of vitamin D are of course an important index of exposure to the sun).

However the PRIME team did not put this conjecture into print and it has never been followed up as a further and vital investigation. What a wasted opportunity!

There is however a similar but much less comprehensive study of vitamin D and CHD death within France. I will put this into a future Post.


Evans AE, Ruidavets J-B, McCrum EE, et al. Autres pays, autres coeurs! Dietary patterns, risk factors and ischaemic Heart disease in Belfast and Toulouse. QJMed 1995; 88: 469-477.

The PRIME study group (prepared by JWG Yarnell). The PRIME study: classical risk factors do not explain the severalfold differences in risk of coronary Heart disease between France and Northern Ireland. QJMed 1998; 91: 667-676.