Inge Groenendijk

Bone is a living tissue that changes over the course of a lifetime. During ageing, bone mass decreases and bone gets more porous. If too much bone mass is lost, this leads to the development of osteoporosis. Osteoporosis increases the risk of falls and fractures, which in turn leads to an increase in morbidity and mortality, loss of independence, and a decreased quality of life. It has been well established that consumption of sufficient calcium and vitamin D are required for proper bone health. However, there are more nutrients and nutritional strategies that may play an important role in maintaining and improving bone health in later life, including increasing the intake of protein, magnesium, and dairy. The potential impact of these nutritional strategies to delay or prevent the development of osteoporosis and, as such, support bone health remains understudied. The aim of this thesis was to investigate the role of nutritional factors in supporting bone health of older adults.

Chapter 2 focused on the role of dietary protein intake in bone health of older adults. The systematic review in Chapter 2.1 uncovered a positive trend between higher protein intakes and higher femoral neck and total hip bone mineral density (BMD), and the meta-analysis showed that higher protein intakes resulted in a significant decrease in hip fractures (pooled HR 0.89). In Chapter 2.2, total and animal protein intake were associated with higher BMD in the total body and spine (beta ranging from 0.0011 to 0.0017 g/cm2). In contrast, higher plant protein intake was associated with lower total body and spine BMD (beta -0.0010 and -0.0019 g/cm2, respectively). Interventions of 12 or 24 weeks with protein supplementation or protein supplementation combined with resistance exercise did not lead to significant improvements in BMD. Chapter 2.3 showed that supplementation of 31 g whey protein for 20 weeks had no effect on BMD after 20 weeks and 1 year in prostate cancer patients on androgen deprivation therapy.

In Chapter 3, the nutritional factors magnesium, dairy and a milk supplement were addressed. The systematic review in chapter 3.1 indicated that a higher magnesium intake may support an increase in hip and femoral neck BMD. The meta-analysis showed a significant positive association between magnesium intake and hip BMD (pooled beta 0.03). Evidence from randomized controlled trials was missing. In Chapter 3.2, it was concluded that the results from a large intervention study in Australia were translatable to the Dutch population; increasing the intake of dairy products (leading to a calcium intake of 1100-1200 mg/d and protein intake of 1.1 g/kg/d) may be beneficial for the bone health of aged care residents in the Netherlands. Chapter 3.3 showed that a 24-wk combined nutrition (fortified milk supplement containing protein, calcium, cholecalciferol, and vitamin B-12) and exercise intervention successfully improved vitamin B-12 and 25-hydroxyvitamin D concentrations as well as the balance of bone turnover markers of Chinese middle-aged and older adults.

In Chapter 4, insights emerging from studies in hip fracture patients are presented. Hip fracture patients are more vulnerable than healthy older adults are. Therefore, the role of nutritional factors to support bone health may be different in this population. Chapters 4.1 and 4.2 showed that protein intake was <0.8 g/kg/d in about half of the patients and <1.2 g/kg/day in more than 90% of the patients. Regarding micronutrients, mean intakes of calcium, vitamin D, potassium, magnesium, and selenium were significantly below the recommendations. The combined prevalence of risk of malnutrition and malnourishment increased from 20% of the patients at hospital admission to 64% at 3 months (Chapter 4.2). In geriatric rehabilitation wards, 73% of the older hip fracture patients were classified as either malnourished or at risk of malnutrition (Chapter 4.1). Furthermore, approximately one third had low muscle mass and a quarter showed low muscle strength. Chapter 4.2 concluded that good nutritional status comes with higher BMD in older hip fracture patients, but no association was found for protein with bone health outcomes. Based on this thesis, protein appears to have the greatest potential for supporting bone health in older adults, next to calcium and vitamin D. Dairy products are a suitable source for achieving adequate protein and calcium intakes. However, the added value of a high magnesium intake for supporting bone health remains unclear. Due attention for nutritional strategies is needed to improve dietary intake, nutritional status, and clinical outcomes in hip fracture patients. This thesis provides valuable insights into the field of nutrition and bone health, which is essential to delay or prevent the development of osteoporosis, reducing the risk of fractures, and maintaining mobility and independence in later life. Therefore, research into bone health contributes to promoting healthy ageing and the overall well-being of older adults.