Excess retinol intake may explain the high incidence of osteoporosis in northern Europe

Restricting vitamin A intake increases bone formation in Zambian children with high liver stores of vitamin

This analysis was performed in Zambian children who had a high prevalence of hypervitaminosis A, defined as > 1.0 μmol retinol/g liver. Bone parameters included markers of bone formation (P1NP), bone resorption (CTX), parathyroid hormone, calcium, vitamin A, and vitamin D. Low dietary vitamin A intake increased P1NP.

PURPOSE

Vitamin A (VA) interacts with bone health, but mechanisms require clarification. In countries where multiple interventions exist to eradicate VA deficiency, some groups are consuming excessive VA. Bone metabolism and inflammatory parameters were measured in Zambian children who had high prevalence of hypervitaminosis A determined by ¹³C-retinol isotope dilution.

METHODS

Children (n = 143), 5 to 7 years, were recruited into a placebo-controlled biofortified orange maize feeding study for 90 days. Bone turnover (P1NP and CTX) and inflammatory (C-reactive protein (CRP) and alpha-1-acid glycoprotein) biomarkers were measured in fasting blood samples before and/or after intervention with the following: (1) VA at the recommended dietary allowance (400 μg retinol activity equivalents/day (as retinyl palmitate)), (2) maize enhanced with the provitamin A carotenoid β-carotene (2.86 mg/day), or (3) a placebo. Parathyroid hormone, calcium, and 25(OH)-vitamin D were measured at end line.

RESULTS

Bone formation, as measured by P1NP, increased (P < 0.0001) in the placebo group who consumed low preformed VA during the intervention. Bone resorption, measured by CTX, was not affected. P1NP and CTX were negatively associated with inflammation, most strongly with CRP. Serum calcium did not differ among groups and was low (7.29 ± 0.87 μg/dL). Serum 25(OH) D did not differ among groups (54.5 ± 15 nmol/L), with 91% < 75 nmol/L and 38% < 50 nmol/L.

CONCLUSIONS

Reduction of dietary preformed VA in Zambian children for 4 months improved bone formation. Chronic consumption of preformed VA caused hypervitaminosis A and may impair bone formation. In children, this could be associated with failure to accrue optimal peak bone mass.

TRIAL REGISTRATION

The NIH Clinical Trial registry number is NCT01814891; https://clinicaltrials.gov/ct2/show/NCT01814891 .

Vitamin A decreases the anabolic bone response to mechanical loading by suppressing bone formation

Increased vitamin A consumption is associated with decreased cortical bone mass and increased fracture risk in humans. Rodent studies have demonstrated that hypervitaminosis A increases cortical bone resorption, whereas the importance of the effects on bone formation is less well defined. We used an experimental model of increased bone formation by loading of the tibiae to investigate the effect of vitamin A on bone formation. Control [retinol activity equivalents (RAE) 4.5 µg/g chow] or vitamin A (RAE 60 µg/g chow) diets were given to female C57BL/6N mice for 4 wk, after which the tibiae were subjected to axial loading on alternate days for 2 wk, while the diets were continued. Vitamin A inhibited the loading-induced increase in trabecular and cortical bone volume. This was attributed to inhibition of loading-induced increase in osteoblast number and activity, and expression of osteoblastic genes Sp7, Alpl, and Col1a1 in cortical bone. Vitamin A, loading, and combination thereof also resulted in site-specific effects on bone composition measured by Raman spectroscopy. In summary, a clinically relevant dose of vitamin A suppresses the loading-induced gain of bone mass by decreasing bone formation. These observations may have implications for regulation of bone mass caused by physical activity and the risk of osteoporosis in humans.-Lionikaite, V., Henning, P., Drevinge, C., Shah, F. A., Palmquist, A., Wikström, P., Windahl, S. H., Lerner, U. H. Vitamin A decreases the anabolic bone response to mechanical loading by suppressing bone formation.

Clinically relevant doses of vitamin A decrease cortical bone mass in mice

Excess vitamin A has been associated with decreased cortical bone thickness and increased fracture risk. While most studies in rodents have employed high dosages of vitamin A for short periods of time, we investigated the bone phenotype in mice after longer exposure to more clinically relevant doses. For 1, 4 and 10 weeks, mice were fed a control diet (4.5 µg retinyl acetate/g chow), a diet modeled from the human upper tolerable limit (UTL; 20 µg retinyl acetate/g chow) and a diet three times UTL (supplemented; 60 µg retinyl acetate/g chow). Time-dependent decreases in periosteal circumference and bone mineral content were noted with the supplemented dose. These reductions in cortical bone resulted in a significant time-dependent decrease of predicted strength and a non-significant trend toward reduced bone strength as analyzed by three-point bending. Trabecular bone in tibiae and vertebrae remained unaffected when vitamin A was increased in the diet. Dynamic histomorphometry demonstrated that bone formation was substantially decreased after 1 week of treatment at the periosteal site with the supplemental dose. Increasing amount of vitamin A decreased endocortical circumference, resulting in decreased marrow area, a response associated with enhanced endocortical bone formation. In the presence of bisphosphonate, vitamin A had no effect on cortical bone, suggesting that osteoclasts are important, even if effects on bone resorption were not detected by osteoclast counting, genes in cortical bone or analysis of serum TRAP5b and CTX. In conclusion, our results indicate that even clinically relevant doses of vitamin A have a negative impact on the amount of cortical bone.

Dairy products and bone health: how strong is the scientific evidence?

The relevance of dairy produce for the diminishment of osteoporotic risk is still a matter of scientific debate due to the outcome of a few single observational studies. This review will address the most robust point estimate on the role of dairy products, as reported in systematic reviews and meta-analyses on randomised controlled trials in the case of bone mineralisation or prospective studies in the case of fracture risk. Plain dairy products or those fortified with Ca and/or vitamin D improve total body bone mineral content (BMC) by 45-50 g over 1 year when the daily baseline Ca intake is lower than 750 mg in Caucasians and Chinese girls. In Caucasian and Chinese women, Ca from (fortified) dairy products increases bone mineral density (BMD) by 0·7-1·8 % over 2 years dependent on the site of measurement. Despite the results on BMC, there are currently no studies that have investigated the potential of dairy products to reduce fracture risk in children. In adult Caucasian women, daily intake of 200-250 ml of milk is associated with a reduction in fracture risk of 5 % or higher. In conclusion, the role of dairy products for BMC or BMD has been sufficiently established in Chinese and Caucasian girls and women. In Caucasian women, drinking milk also reduces fracture risk. More research on the role of dairy products within the context of bone health-promoting diets is needed in specific ethnicities, other than Chinese and Caucasians, and in men.

Retinoic acid exacerbates chlorpyrifos action in ensuing adipogenic differentiation of C3H10T½ cells in a GSK3β dependent pathway

The cell differentiation can be exploited as a paradigm to evaluate the effects of noxious chemicals, on human health, either alone or in combinations. In this regard, the effect of a known cell differentiation agent, retinoic acid (RA) was analyzed in the presence of a noxious chemical chlorpyrifos (CPF), an organophosphate (OP), the receptors of which have recently been localized to mesenchymal stem cells (MSCs). The observed imbalance of adipogenic to skeletal differentiation by CPF together with conundrum about adipogenic potential of RA prompted us to delineate their combinatorial effects on C₃H₁₀T½MSC-like undifferentiated cells. Based on MTT assay, the cellular viability was retained by CPF at concentrations ranging from 0.01–50μM, beyond which it caused cytotoxicity. These non-toxic concentrations also mildly interfered with adipogenesis of C₃H₁₀T½ cells following exposure to adipogenic cocktail. However, upon exposure to RA alone, these MSCs adopted elongated morphology and accumulated lipid vesicles, by day 20, as discerned by phase-contrast and transmission electron microscopy (TEM), in concert with enhanced Oil Red O stained cells. This effect got strongly augmented upon exposure to combination of CPF and RA in a dose-dependent manner. Simultaneous up-regulation in perilipin-1 (PLIN1) and adipsin (ADN) genes, additionally reiterated the adipogenic differentiation. Mechanistically, GSK3β pathway was found to be a major player, whereby inhibiting it with lithium chloride (LiCl) resulted in complete blockage of lipid accumulation, accompanied by complete down regulation of PLIN1 and ADN gene expression. In conclusion, these observations for the first time, lend evidence that exposure of CPF accompanied by RA directs commitment of C₃H₁₀T½ cells to adipogenic differentiation through a process involving a crosstalk at GSK3β signaling.

Lower prevalence of hip fractures in foreign-born individuals than in Swedish-born individuals during the period 1987-1999

Background

This is the first longitudinal study with a 22-year follow-up, based on a national and complete sample, to determine whether the prevalence of hip fracture and the age when it occurs are influenced by migration and by being foreign-born. Cultural background and environmental factors such as UV-radiation and lifestyle during childhood and adolescence may influence the risk of a hip fracture event later in life. Differences in prevalence might occur between the indigenous population and those who have migrated to a country.

Methods

The study was based on national population data. The study population consisted of 321,407 Swedish-born and 307,174 foreign-born persons living in Sweden during the period 1987-1999.

Results

Foreign-born individuals had a reduced risk of hip fracture, with odds ratios (ORs) of 0.47-0.77 for men and 0.42-0.88 for women. Foreign-born women had the hip fracture event at a higher age on average, but a longer time spent in Sweden was associated with a small but significant increase in risk.

Conclusions

We found that there was a reduced risk of hip fracture in all foreign-born individuals, and that the hip fracture event generally happened at a higher age in foreign-born women. Migration must therefore be considered in relation to the prevalence and risk of hip fracture. Migration can therefore have a positive effect on one aspect of the health of a population, and can influence and lower the total cost of healthcare due to reduced risk and prevalence of hip fracture.

Vitamin A intake and the risk of hip fracture in postmenopausal women: the Iowa Women's Health Study

Excessive intake of vitamin A is postulated to have a detrimental effect on bone by inducing osteoporosis. This may lead to an increased risk of fracture, particularly in persons who are already at risk of osteoporosis. However, few studies have specifically examined the association of vitamin A intake through diet and supplement use, with fractures in a cohort of older, community-dwelling women. We prospectively followed a cohort of 34,703 postmenopausal women from the Iowa Women's Health Study to determine if high levels of vitamin A and retinol intake through food and supplement use were associated with an increased risk of hip or all fractures. A semiquantitative food frequency questionnaire was used to obtain the participants' baseline vitamin A and retinol intake. Participants were followed for a mean duration of 9.5 years for incident self-reported hip and nonhip fractures. After multivariate adjustment, it was revealed that users of supplements containing vitamin A had a 1.18-fold increased risk of incident hip fracture (n = 525) compared with nonusers (95% CI, 0.99 to 1.41), but there was no evidence of an increased risk of all fractures (n = 6,502) among supplement users. There was also no evidence of a dose-response relationship in hip fracture risk with increasing amounts of vitamin A or retinol from supplements. Furthermore, our results showed no association between vitamin A or retinol intake from food and supplements, or food only, and the risk of hip or all fractures. In conclusion, we found little evidence of an increased risk of hip or all fractures with higher intakes of vitamin A or retinol among a cohort of older, postmenopausal women.