Department of Epidemiology and Biostatistics (252), PO Box 9101, 6500 HB Nijmegen, The Netherlands.
SirsThe discussion between Bertuzzi et al.1 and Fernández Jarne et al.2 concerning non-fatal myocardial infarction (AMI) and olive oil consumption in Italy and Spain highlighted the controversy. In three of the four Mediterranean case-control studies, two in Italy and one in Greece, any support for a strong inverse relation between olive oil and coronary heart disease (CHD) was lacking; in contrast, an inverse association was reported in Spain.2 This inverse association has been put in the public domain and both research groups agree that this association remains open to discussion.
People who eat large quantities of saturated fat, in the form of butter, cheese, and other milk products, often have one of the lowest rates of cardiovascular disease and too many disturbing paradoxes, such as the so-called French, Italian and Albanian paradoxes, remain vexatious and provocative.3 Life in Mediterranean countries might be protective, but the time has come for a major paradigm shift of ecological differences in health outcomes: not the olive, i.e. the lifestyle and behaviour might be essential in the causation of cardiovascular heart diseases (CVD), but the geographical location, i.e. where the olive grows.4 A geographical South-to-North gradient in the prevalence of CHD within countries demands attention, e.g. in Great Britain5 and France,6 and on a still more intricate scale, among countries at different latitudes, such as Italy, The Netherlands and Finland,7 or France versus Northern Ireland.8
A similar geographical gradient has been established in many constitutional diseases and very different countries, e.g. schizophrenia,9 suicide,10 and prostate,11 breast,12 and other cancers.13 This latitude effect in incidence increases away from the Equator, not only in the Northern hemisphere, but also in the Southern hemisphere, as for example, in fatal neural tube defects14 and diabetes type 1.15 All these conditions are characterized not only by this latitude effect, but also by seasonality of birth.16,17 This connection reveals an interesting causal relationship between these conditions and the ovulatory pattern, and in particular to pathological conceptions.
The consistent and predictable relations between the South-to-North gradient and timing of mating seasons in cats,18 non-human19 and human primate populations20,21 indicates seasonality of the ovulatory rate. The so-called seasonally pre-ovulatory overripeness ovopathy (SPrOO-)hypothesis states that optimal or high-quality oocytes coincide with the peaks of this ovulatory pattern, the less-optimal and poor quality ones appearing in the transitional stages between the ovulatory seasons.16,17 The (patho-)physiological processes of oocyte maturation in animals22,23 and the circumstantial evidence of similar phenomena in humans16,17,24 explain these seasonally bound coincidences. The further from the Equator, the stronger the seasonality of the ovulatory pattern and the higher the rate of non-optimal conceptions. Geographical latitude and its intricate relation to seasonality of birth reveals new mechanisms and disease pathways and, in addition, the ability to explain social, geographical, and temporal patterns of disease distribution.16,17
References
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