Short wavelength mortality cycles, with a period of about 5 to 6 years, were described in Chapter 3; in this and succeeding chapters we consider them in more detail and show that they occurred commonly in a variety of different communities (see section 15.1) and that, in some instances, lethal infectious epidemics were superimposed on the peaks of the oscillations. What external factors drove these exogenous mortality cycles? One thesis, developed further in Chapters 7 and 8, is that mortality, particularly among children and infants, is sensitive to the subtle effects of fluctuating malnutrition. Obviously, outright famine caused deaths, as described in the parish registers of Greystoke in Cumberland in 1623, but disasters on this scale seem to have been rare, even in the marginal economies of the northwest. Rather, we have used time-series analysis and other statistical techniques to show that an inadequate diet, perhaps lacking in nutritive value, vitamins or trace elements had serious, and hitherto undetected, direct and indirect effects on pregnancy, neonatal, post-neonatal and childhood mortality, and susceptibility to disease.

It is suggested that the annual grain prices provide a good measure of the fluctuations in nutritive levels, particularly among the poorer sections of a community and that, in certain circumstances, the annual price of grains interacted with the price of other commodities to produce years of particular hardship (see Chapter 8). Communities living under marginal farming conditions would be particularly susceptible in such hardship years.

Grain prices in past centuries were subject to violent fluctuations from one year to another, although some regularity in the longer-term movement of prices has been discerned.