Milk-and-Dairy-Products-in-Human-Nutrition-FAO

Chapter 4 – Milk and dairy products as part of the diet 121
in dairy products was associated with CHD or stroke mortality, although childhood
calcium intake was inversely associated with stroke mortality. Childhood diets rich
in dairy or calcium were associated with lower all-cause mortality in adulthood,
independent of childhood height (a marker for IGF levels in childhood), which suggests
that the IGF pathway was not involved as an underlying mechanism. However,
the authors speculate that childhood diets may have had long-term programming
effects on adult IGF-1 levels, which may not be reflected by childhood height.
4.4 Dietary dairy and bone health
4.4.1 Bone growth
The process of bone resorption and bone formation is termed bone remodelling.
This process takes place throughout life, although at different rates at different times
(Figure 4.1).
Bone mass increases rapidly during adolescence (Figure 4.1). During this period
of rapid growth, approximately half of adult peak bone mass (PBM) is accumulated
(Heaney et al., 2000) and bone turnover rates are high, with bone formation exceeding
bone resorption rates. Bones elongate and height increases under the control
of genes that programme body size through changes in sex steroid hormones
and growth hormones (Weaver, 2002). There is a lag period between peak height
velocity and peak bone mineral content velocity when children in early puberty
have relatively low bone mass (Bailey et al., 1999). This is consistent with a period
of high incidence of fracture (Khosla et al., 2003). Peak bone mass (the maximum
amount of bone mass attained during a person’s life) can be reached as early as the
late teenage years or as late as mid-thirties, depending on skeletal site (Theobald,
2005). A 10 percent increase in PBM is associated with a 50 percent reduction in
risk of osteoporotic fracture (Bonjour et al., 2003, cited in Theobald, 2005). From
figure 4.1
Changes in bone mass during the human life cycle
Attainment of PBM
Consolidation
Age-related bone loss
Bone mass
Men
Women
0 10 20 30 40 50 60 70
Age (years)
Critical times are: (1) attainment of peak bone mass (PBM: 0–28 years of age, with pubertal years being particularly crucial);
(2) menopause (•; during the menopause and ≤ 10 years post menopause it is estimated that 1–2 percent of bone is lost per
year); (3) age-related bone loss (a low bone mineral density threshold increases osteoporosis fracture risk).
Source: Lanham-New, 2008.