small RCTs. There is little evidence that levels of calcium intake above that needed for neutral calcium balance are consistent with an improvement in BMD. Of note, the pregnancy-induced increase in fractional calcium absorption allows the needs of pregnancy to be met without an increase in calcium intake above normal requirements. Although it does result in bone resorption, lactation does not increase the risk of reduced BMD or osteoporosis.
Osteomalacia, as explored in one recent study, is not found to be meaningfully present until serum 25OHD levels are at or below at least 30 nmol/L and is rarely present when serum 25OHD levels are above 50 nmol/L, suggesting the possibility of a population distribution. Further, fractional calcium absorption is not additionally enhanced when serum 25OHD levels are above 50 nmol/L. Both osteomalacia and fractional calcium absorption are, thus, informative for the development of DRIs for vitamin D in periods of bone maintenance.
Finally, calcium and vitamin D requirements are not increased during pregnancy or lactation. Nor does vitamin D supplementation alter the development of the fetal, infant, or maternal skeletal health outcomes.
Bone loss A sustained bone loss is associated with the normal aging process and with menopause, as discussed in Chapter 2. The older adult loses bone at an estimated 1 percent per year (Sowers et al., 2010), although the rate of loss varies. The loss is abrupt for women at menopause and is quite rapid until approximately the sixth or seventh year after the onset of menopause. For men, bone loss begins later in life and generally declines steadily over time. Although neutral calcium balance is desired, the realities focus on reducing bone loss and mitigating the degree of negative calcium balance to the extent possible.
Calcium balance Bone loss is reflected by negative calcium balance, and ideally the degree of negative calcium balance would be reduced to the extent possible. Therefore, a reasonable starting point for considering the nutrient intake levels that may be relevant during the life stages associated with bone loss is information on calcium balance. However, relatively few data are available. The study conducted by Hunt and Johnson (2007), described previously, included a few older men up to the age of 64 years and some older women up to the age of 75 years. Specifically, information provided by the study authors6 indicated that there were 2 men and 34 women between 51 and 70 years of age and 4 women more than 70 years of age. The Hunt and Johnson (2007) analysis suggested that, overall, per-