Epidemiological and prospective studies largely support the link between calcium intake and reduced fracture prevalence. Warensjo et al. (2011) conducted a longitudinal study on 61,000 women, using food frequency questionnaires, and found intake below 700mg/d was associated with increased fracture rates. However, the accuracy of self-administered food records is questionable. Schaefer et al. (2000) suggested such methods are highly vulnerable to both under-reporting and socially desirable reporting.
Thus, such studies are unlikely to have accurately observed calcium intake at a population level. Thus, it is difficult to draw firm conclusions from this literature body. Few studies have been able to observe significant benefits for calcium intake over 400mg/d-500mg/d (DOH, 1998; Dawson-Hughes et al. , 1990). This was demonstrated by Hannan et al. (2000) who supplemented 800-mg/d in an elderly cohort during a 4-year longitudinal study; the only developments in bone loss and fracture rates, occurred in those who initially consumed an insufficient amount.
Similar effects have been observed from studies in southern Europe, reviewing the effects of dietary calcium through milk and cheese consumption (Kanis et al. , 1999). Taken together, the evidence body suggests whilst a calcium deficiency can be more heavily associated with fracture risk; there is limited evidence to suggest high levels of calcium results in lower than average fracture rates. However, fracture rates cannot be considered an absolute measure for osteoporosis. As identified by Rizzoli et al. (2009) fractures occur because of a multitude of factors.
Thus, wider research is required to confirm the effects of calcium. The link between calcium intake and BMD has been widely researched. Some studies have observed relative increases in BMD (up to 3%) when supplementing high levels of calcium (Dawson-Hughes et al. 1990). However, meta-analysis have concluded that on average the magnitude of effect is minimal (Cumming and Kleinberg, 2004). High-calcium intake trials have typically demonstrated an effect size of approx. -imately 1% on BMD (Welton, Kemper and VanStavrin, 2005).
Although calcium is used extensively in bone capital accumulation, direct intake will not always have a significant impact on bone tissue. According to Jackson et al. (1995) calcium retention is limited, and thus, the body can only utilise a fraction of what it consumes. Although calcium is commonly recommended to enhance skeletal health, it may be more beneficial to identify methods that can yield greater calcium retention. Some studies providing focus on specific parts of the population have yielded greater results. Hwadmin et al.
(1994) found calcium intake was a significant predictor of peak bone mass in adolescents; it was also identified that participants consuming between 800mg/d-1200mg/d had a BMD 4. 7% greater than those consuming less than 700mg/d. Furthermore, in a follow up study it was identified that peak BMD acquired during adolescence had a positive impact on BMD during adulthood (Hwadmin et al. 2004). Thus, the overall importance of calcium intake during puberty is considerably high. In addition, Rizzoli et al. (2013) found calcium intake over 800mg/d slowed bone resorption by 8.
7% in menopausal women, and thus, reduced the likelihood of osteoporosis. In light of this evidence, the importance of individualised recommendations is apparent. Some research has identified that physical activity is capable of improving mineral retention (Rizzoli et al. 2010). Weight-bearing exercises specifically, have been recognised a method for increasing mineral utilisation (Gardner, Rober-tson and Campbell, 2000). Thus, physical activity should be widely considered before recomm-ending certain nutrients.
However, the research body that surrounds the effects of physical activity on individual nutrients is limited. As a result of this, it is difficult to make firm recom-mendations with relation to using exercise to maximise mineral retention. Future research could identify that calcium is capable of a greater effect size when combined with an exercise regimen. Taken together, evidence suggests between 400mg/d and 500mg/d of calcium may provide some protective properties to the skeletal system.
However, measures of BMD suggest the overall value of calcium intake across the general population is debatable. Wider studies on spec-ific parts of the population, yielded a greater effect size, and thus, calcium intake could be considered more important within these populations. Evidence indicated intakes greater than 800mg/d could be beneficial to adolescents and menopausal women. Furthermore, research on wider modifiable risk factors suggested calcium intake may be more beneficial when combined with physical activity.