The Hertfordshire Cohort Study (HCS) and Hertfordshire Ageing Study (HAS)

The HALCyon programme uses two cohorts assembled by the Medical Research Council Lifecourse Epidemiology Unit at the University of Southampton: the Hertfordshire Cohort Study and the Hertfordshire Ageing Study.

A determined midwife sets the scene for significant breakthroughs…

In the early twentieth century there was widespread concern about the physical deterioration of the British people. In 1911, Ethel Margaret Burnside (Hertfordshire’s first “chief health visitor and lady inspector of midwives”) assembled a team of midwives and nurses charged with improving the health of children in Hertfordshire. 

A midwife attended women during childbirth and recorded the birth weight of their offspring on a card. A health visitor subsequently went to each baby’s home throughout its infancy and recorded its illnesses and vaccinations, development and method of infant feeding and weaning; the baby was then weighed again at one year of age. This information was transcribed into ledgers at the Hertfordshire county office (Figure 1). The ledgers cover all births in Hertfordshire from 1911 until the NHS was formed in 1948.

Scouring the basements…

Families' weekly food diary

Ecological studies conducted in the 1980’s demonstrated a close geographic correlation between death rates from coronary heart disease during 1968-78 in different parts of England and Wales and the infant mortality rate in those areas sixty years previously.  These studies suggested that adverse environmental influences acting in utero and during infancy might increase the risk of cardiovascular disease in later life. However, this hypothesis required investigation using data on individuals.

As part of a nationwide search of archives, staff working at the MRC Unit, University of Southampton, discovered the Hertfordshire ledgers.

Establishing the studies

The ledgers were computerised and linked to mortality records using the National Health Service Central Register (NHSCR). In the early 1990’s, surviving men and women who were born between 1920 and 1930 and still resident in Hertfordshire were contacted through their General Practitioner and those who were willing underwent detailed physiological investigations to explore lifecourse influences on adult disease. 717 men and women resident in North Hertfordshire attended home interviews and clinics where a wide range of markers of ageing were characterised. These clinics comprised the first follow-up of the Hertfordshire Ageing Study (HAS) which was the first to demonstrate that size in early life is associated with markers of ageing in older people. In 2004 a second follow-up of the HAS cohort was carried out. The principal objective of the Hertfordshire Ageing Study is to examine life course influences on healthy ageing, with sarcopenia, frailty, falls, physical performance and cognitive function as the principal outcomes of interest. 

In 1998, a larger and younger cohort of surviving men and women born in Hertfordshire between 1931-39 and still living there were recruited to home interviews and clinics for the Hertfordshire Cohort Study (HCS). The principal objective of HCS is to evaluate the interactions between the genome; the intra-uterine and early postnatal environment;  and adult diet and lifestyle in the aetiology of chronic diseases in later life (cardiovascular disease, type II diabetes mellitus and obesity; osteoporosis, osteoarthritis and sarcopenia).

The HCS and HAS birth cohorts are completely distinct (with birth years ranging 1931-39 for HCS and 1920-30 for HAS) and have different, although related, research objectives. The HALCyon prpgramme uses information from both studies.

What data are available in HCS and HAS?

A guide to the extensive data available in HCS and HAS is available.

Key findings from the Hertfordshire studies

Mortality

The combined 1911-39 Hertfordshire birth records were used to create a mortality database of 37 000 men and women; 7916 had died by the end of 1999. Higher birth weight was associated with decreased risk of circulatory disease mortality in men and women, and with decreased risk of mortality from accidental falls in men, and decreased risk of mortality from pneumonia, injury, diabetes, and musculoskeletal disease in women. This was not counterbalanced by an increased risk of other causes of death.

Osteoporosis 

In the HCS DXA study, birth weight was associated with bone mineral content in men and women, and relationships with weight at one year were even stronger. Models of DXA measurements on weight at birth, one year and adulthood demonstrated that weight at each of these points in the life course is important in the determination of adult bone mass, with greater contributions of earlier growth to bone size and mineral content, than to bone mineral density.    

Sarcopenia

Grip strength was strongly associated with birth weight in HCS men and women, independently of adult height and weight. Associations with infant growth were weakened after allowing for adult size. These results suggest that sarcopenia may have its origins in early life, with influences of infant growth mediated through adult size.   

Physical performance and physical activity 

The was little evidence in HCS for early life influences on levels of physical activity and physical performance in later life. However, there were strong relationships between physical activity and physical performance, emphasizing the importance of remaining active in later life. 

Diet

HCS data were used to explore the relationships between total and saturated fat and serum cholesterol. The adverse effects of high intakes of dietary fat were found to be confined to those with lower birth weights. HCS data have also showed a clear association between higher intakes of oily fish (with associated higher levels of vitamin D) and higher grip strength.

Ageing

The first HAS follow-up showed that lower birth weight was related to sarcopenia in later life, and lower weight at one year of age was related to sarcopenia, lens opacity, skin thickness and hearing threshold. This phase of the study also demonstrated that different systems of the same individual do not age together, suggesting that further research was, and still is, needed to identify the different processes underlying ageing.  Further work explored whether chronological age or grip strength might function as useful single markers of frailty and concluded that, within the relatively narrow age range studied, grip strength was associated with more markers of frailty than chronological age; raising the possibility that grip strength might serve as a useful marker of frailty in clinical practice.

Further reading

The Hertfordshire Studies home page: http://www.mrc.soton.ac.uk/herts/ 

HE Syddall, A Aihie Sayer, EM Dennison, H J Martin, DJP Barker, C Cooper and the Hertfordshire Cohort Study Group. Cohort Profile: The Hertfordshire Cohort Study. Int J Epidemiol. 2005 Dec;34(6):1234-42.