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This article delves into the contributions of Milton Santos (1926–2001) to the economic study of entrepreneurship. Santos made contributions to spatial economics, urbanization, and planning theories, being an important author to the field of regional and urban economics. His most famous idea is the “two circuits” of the urban economy. According to this approach, the urban economies in peripheral countries create two economic-urban circuits that are both distinct and connected. The superior circuit comes from the technological modernization and cultivates international relationships. High-value goods and networks and new technologies circulate through it. The inferior circuit works outside these networks. It consists of low-dimension activities from local populations. Santos elaborated this theory to understand urbanization in peripheral countries and to give voice to the ones left behind by the development process. He did not write directly on entrepreneurship. We argue, however, that his thoughts can be important to entrepreneurship studies. The entrepreneurship discourse, that had in Schumpeter one of its main sources, assumes that the entrepreneur has traits related to the superior circuit, such as access to resources and networks, which would not be available to entrepreneurs in the inferior circuit. We argue that Santos’ contributions can inform economic thought in entrepreneurship by calling attention to how literature can approach structural problems and contribute to making economics a more diverse discipline.

Because of the importance of having enough sleep in life and health, this study aims to determine the effect of vitamin D supplementation on sleep quality and pregnancy symptoms (primary outcomes) and side effects (secondary outcome).

In this triple-blind randomized controlled clinical trial, 88 pregnant women with gestational age of 8–10 weeks and serum vitamin D concentration less than 30 ng/ml were allocated into vitamin D (n = 44) and control (n = 44) groups by blocked randomization method. The vitamin D group received a 4,000 IU vitamin D pill, and the control group received a placebo pill daily for 18 weeks. Independent t-, Mann–Whitney U and ANCOVA tests were used to analyze the data.

The post-intervention mean (SD: standard deviation) of total sleep quality score in the vitamin D and placebo group were 1.94 (2.1) and 4.62 (1.71), respectively. According to the Mann–Whitney U test, this difference between the two groups was statistically significant (p < 0.001). The mean (SD) of pregnancy symptoms in the vitamin D and placebo groups was 23.95 (16.07) and 26.62 (13.84), respectively, and there was no significant difference between the two groups based on ANCOVA test (p = 0.56). Considerable side effects were not observed in any groups.

This study was conducted due to the contradictory results of the effect of vitamin D on sleep quality and the high prevalence of sleep disorders and pregnancy symptoms.