Too much vitamin A may increase risk of bone fractures

Date: October 9, 2018 Source: Society for Endocrinology Summary: Consuming too much vitamin A may decrease bone thickness, leading to weak and fracture prone bones, according to a new study in mice.

Consuming too much vitamin A may decrease bone thickness, leading to weak and fracture prone bones, according to a study published in the Journal of Endocrinology. The study, undertaken in mice, found that sustained intake of vitamin A, at levels equivalent to 4.5-13 times the human recommended daily allowance (RDA), caused significant weakening of the bones, and suggests that people should be cautious of over-supplementing vitamin A in their diets.

Vitamin A is an essential vitamin that is important for numerous biological processes including growth, vision, immunity and organ function. Our bodies are unable to make vitamin A but a healthy diet including meat, dairy products and vegetables should be sufficient to maintain the body's nutritional needs. Some evidence has suggested that people who take vitamin A supplements may be increasing their risk of bone damage. Previous studies in mice have shown that short-term overdosing of vitamin A, at the equivalent of 13-142 times the recommended daily allowance in people, results in decreased bone thickness and an increased fracture risk after just 1-2 weeks. This study is the first to examine the effects of lower vitamin A doses that are more equivalent to those consumed by people taking supplements, over longer time-periods.

In this study, Dr Ulf Lerner and colleagues from Sahlgrenska Academy at the University of Gothenburg, report that mice given lower doses of vitamin A, equivalent to 4.5-13 times the RDA in humans, over a longer time period, also showed thinning of their bones after just 8 days, which progressed over the ten week study period.

Dr Ulf Lerner commented, "Previous studies in rodents have shown that vitamin A decreases bone thickness but these studies were performed with very high doses of vitamin A, over a short period of time. In our study we have shown that much lower concentrations of vitamin A, a range more relevant for humans, still decreases rodent bone thickness and strength."

Next, Dr Ulf Lerner intends to investigate if human-relevant doses of vitamin A affect bone growth induced by exercise, which was not addressed in this study. Additionally, his team will study the effects of vitamin A supplementation in older mice, where growth of the skeleton has ceased, as is seen in the elderly.

Dr Ulf Lerner cautions: "Overconsumption of vitamin A may be an increasing problem as many more people now take vitamin supplements. Overdose of vitamin A could be increasing the risk of bone weakening disorders in humans but more studies are needed to investigate this. In the majority of cases, a balanced diet is perfectly sufficient to maintain the body's nutritional needs for vitamin A."

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Journal Reference:

Vikte Lionikaite, Karin L Gustafsson, Anna Westerlund, Sara H Windahl, Antti Koskela, Juha Tuukkanen, Helena Johansson, Claes Ohlsson, Herschel H Conaway, Petra Henning, Ulf H Lerner. Clinically relevant doses of vitamin A decrease cortical bone mass in mice. Journal of Endocrinology, 2018; DOI: 10.1530/JOE-18-0316

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Society for Endocrinology. "Too much vitamin A may increase risk of bone fractures." ScienceDaily. ScienceDaily, 9 October 2018. <www.sciencedaily.com/releases/2018/10/181009102538.htm>.

What flowers looked like 100 million years ago

Date: August 2, 2017 Source: University of Vienna Summary: Flowering plants with at least 300,000 species are by far the most diverse group of plants on Earth. They include almost all the species used by people for food, medicine, and many other purposes. However, flowering plants arose only about 140 million years ago, quite late in the evolution of plants, toward the end of the age of the dinosaurs, but since then have diversified spectacularly. No one knows exactly how this happened, and the origin and early evolution of flowering plants and especially their flowers still remains one of the biggest enigmas in biology, almost 140 years after Charles Darwin called their rapid rise in the Cretaceous "an abominable mystery".

Flowering plants with at least 300,000 species are by far the most diverse group of plants on Earth. They include almost all the species used by people for food, medicine, and many other purposes. However, flowering plants arose only about 140 million years ago, quite late in the evolution of plants, toward the end of the age of the dinosaurs, but since then have diversified spectacularly. No one knows exactly how this happened, and the origin and early evolution of flowering plants and especially their flowers still remains one of the biggest enigmas in biology, almost 140 years after Charles Darwin called their rapid rise in the Cretaceous "an abominable mystery."

This new study, the "eFLOWER project," is an unprecedented international effort to combine information on the structure of flowers with the latest information on the evolutionary tree of flowering plants based on DNA. The results shed new light on the early evolution of flowers as well as major patterns in floral evolution across all living flowering plants.

Among the most surprising results is a new model of the original ancestral flower that does not match any of the ideas proposed previously. "When we finally got the full results, I was quite startled until I realized that they actually made good sense," said Hervé Sauquet, the leader of the study and an Associate Professor at Université Paris-Sud in France. "No one has really been thinking about the early evolution of flowers in this way, yet so much is easily explained by the new scenario that emerges from our models."

According to the new study, the ancestral flower was bisexual, with both female (carpels) and male (stamens) parts, and with multiple whorls (concentric cycles) of petal-like organs, in sets of threes. About 20% of flowers today have such "trimerous" whorls, but typically fewer: lilies have two, magnolias have three. "These results call into question much of what has been thought and taught previously about floral evolution!," said Juerg Schoenenberger, a Professor at the University of Vienna, who coordinated the study together with Hervé Sauquet. It has long been assumed that the ancestral flower had all organs arranged in a spiral.

The researchers also reconstructed what flowers looked like at all the key divergences in the flowering plant evolutionary tree, including the early evolution of monocots (e.g., orchids, lilies, and grasses) and eudicots (e.g., poppies, roses, and sunflowers), the two largest groups of flowering plants. "The results are really exciting!" said Maria von Balthazar, a Senior Scientist and specialist of floral morphology and development at the University of Vienna. "This is the first time that we have a clear vision for the early evolution of flowers across all angiosperms."

The new study sheds new light on the earliest phases in the evolution of flowers and offers for the first time a simple, plausible scenario to explain the spectacular diversity of floral forms. Nevertheless, many questions remain. The fossil record of flowering plants is still very incomplete, and scientists have not yet found fossil flowers as old as the group itself. "This study is a very important step toward developing a new and increasingly sophisticated understanding of the major patterns in the evolution of flowers," said Peter Crane, President of the Oak Spring Garden Foundation and a colleague familiar with the results of the study. "It reflects great progress and the results on the earliest flowers are especially intriguing."

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Materials provided by University of Vienna. Note: Content may be edited for style and length.

Journal Reference:

Hervé Sauquet, Maria von Balthazar, Susana Magallón, James A. Doyle, Peter K. Endress, Emily J. Bailes, Erica Barroso de Morais, Kester Bull-Hereñu, Laetitia Carrive, Marion Chartier, Guillaume Chomicki, Mario Coiro, Raphaël Cornette, Juliana H. L. El Ottra, Cyril Epicoco, Charles S. P. Foster, Florian Jabbour, Agathe Haevermans, Thomas Haevermans, Rebeca Hernández, Stefan A. Little, Stefan Löfstrand, Javier A. Luna, Julien Massoni, Sophie Nadot, Susanne Pamperl, Charlotte Prieu, Elisabeth Reyes, Patrícia dos Santos, Kristel M. Schoonderwoerd, Susanne Sontag, Anaëlle Soulebeau, Yannick Staedler, Georg F. Tschan, Amy Wing-Sze Leung, Jürg Schönenberger. The ancestral flower of angiosperms and its early diversification. Nature Communications, 2017; 8: 16047 DOI: 10.1038/NCOMMS16047

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University of Vienna. "What flowers looked like 100 million years ago." ScienceDaily. ScienceDaily, 2 August 2017. <www.sciencedaily.com/releases/2017/08/170802092836.htm>.