Dietary silicon interacts with oestrogen to influence bone health: Evidence from the Aberdeen Prospective Osteoporosis Screening Study

Abstract

Background

Silicon (Si), as Si(OH)₄, is derived mainly from plant-based foods. Dietary Si is associated with bone mineral density (BMD) in premenopausal but not postmenopausal women.

Objective

To examine the association between Si intake and markers of bone health in middle-aged women and to test for interaction with oestrogen status.

Methods

Femoral neck (FN) and lumbar spine (LS) BMD, urinary markers of bone resorption (free pyridinoline and deoxypyridinoline cross-links relative to creatinine, fPYD/Cr and fDPD/Cr) and serum markers of bone formation (N-terminal propeptide of type 1 collagen, P1NP) were measured in a cohort of 3198 women aged 50–62 years (n = 1170 current HRT users, n = 1018 never used HRT). Dietary Si, bioavailable Si and dietary confounders were estimated by food frequency questionnaire.

Results

Mean FN BMD was 2% lower (p < 0.005) in the lowest quartile (Q1) compared to the top quartile of energy-adjusted Si intake (Q4) (mean (SD) Q1, 16 (4.0) mg/d; Q4, 31.5 (7.3) mg/d). Energy-adjusted Si intake was associated with FN BMD for oestrogen-replete women only (late premenopausal women (r = + 0.21, p = 0.03); women on HRT [r = + 0.09, p < 0.001]). There was an interaction between oestrogen status and quartile of energy-adjusted Si intake on FN BMD, which was significant after adjustment for confounders (F = 3.3, p = 0.020), and stronger for bioavailable Si (F = 5.0. p = 0.002). Quartile of energy-adjusted dietary Si intake was negatively associated with fDPD/Cr and fPYD/Cr (p < 0.001) and positively with P1NP (p < 0.05).

Conclusions

This study suggests that oestrogen status is important for Si metabolism in bone health. Further work is required to elucidate the mechanism.

Introduction

The relationship between intake of fruit and vegetables and bone health has been gaining interest over the last decade [1], [2], [3], [4]. The hypothesis that fruit and vegetables may influence bone health because of their acid-balancing properties (which can neutralise the net endogenous acid production (NEAP) of the Western diet) has been questioned [5]. Fruit and vegetables contain a number of components (for example vitamins: vitamin C, folate, and vitamin K, minerals: magnesium [Mg], potassium [K], and other bioactive constituents such as flavonoids) that could plausibly influence bone health [6]. The mineral silicon (Si) is a common component of the diet found mainly in plant-based foods (cereal grains and some fruits and vegetables), drinking water (especially mineral water) and some alcoholic beverages, notably beer [7]. Currently there are no recommended intakes for dietary Si and its role in human health is unclear. Animal and cellular studies have shown that Si is required for normal development of bone and connective tissues [8], [9], [10], [11] but there are few studies examining dietary Si in humans. Osteoporotic subjects who used the dietary Si supplement, monomethyl silane triol, showed an increase in vertebral bone volume [12] and an increase in femoral and vertebral bone mineral density (BMD) [13]. Bone formation (measured by N-terminal propeptide of type 1 collagen, P1NP) was apparently higher in women after one year supplementation with choline-stabilised orthosilicic acid at daily Si doses of 6 mg and 12 mg. In the Framingham offspring cohort an association between dietary Si and hip BMD was found in premenopausal women, which was less strong in men [14]. The study also found no association between dietary Si intake and BMD for postmenopausal women, which suggests that oestrogen (specifically estradiol) may be involved in the relationship between Si and bone health.

Absorption of Si depends on the food source, with Si in green beans and drinking water being particularly well-absorbed (> 50% of the total Si content in the food) in contrast to bananas, where Si is poorly absorbed (2% of the total Si content in bananas) [15]. Adjustment for absorption may better reflect the bioavailability of Si. Single nutrient studies may be criticised because the nutrient being tested could be a marker for other nutrients found in similar dietary sources. Foods that are rich in Si are also a good source of the minerals K and Mg, both of which could potentially influence bone health.

The primary aim of this study was to examine the association between dietary Si intake and markers of bone health in early postmenopausal women (both HRT users and non users) in the UK and to determine whether there was an interaction with oestrogen status. We also tested for the association with bioavailable Si (i.e. following adjustment for absorption) as an a priori planned analysis, and for confounding by other common plant containing minerals, Mg and K.