In utero or early-life vitamin D deficiency is associated with skeletal problems, type 1 diabetes, and schizophrenia, but the prevalence of vitamin D deficiency in U.S. pregnant women is unexplored. We sought to assess vitamin D status of pregnant women and their neonates residing in Pittsburgh by race and season. Serum 25-hydroxyvitamin D (25(OH)D) was measured at 4-21 wk gestation and predelivery in 200 white and 200 black pregnant women and in cord blood of their neonates. Over 90% of women used prenatal vitamins. Women and neonates were classified as vitamin D deficient [25(OH)D<37.5 nmol/L], insufficient [25(OH)D 37.5-80 nmol/L], or sufficient [25(OH)D>80 nmol/L]. At delivery, vitamin D deficiency and insufficiency occurred in 29.2% and 54.1% of black women and 45.6% and 46.8% black neonates, respectively. Five percent and 42.1% of white women and 9.7% and 56.4% of white neonates were vitamin D deficient and insufficient, respectively. Results were similar at <22 wk gestation. After adjustment for prepregnancy BMI and periconceptional multivitamin use, black women had a smaller mean increase in maternal 25(OH)D compared with white women from winter to summer (16.0+/-3.3 nmol/L vs. 23.2+/-3.7 nmol/L) and from spring to summer (13.2+/-3.0 nmol/L vs. 27.6+/-4.7 nmol/L) (P<0.01). These results suggest that black and white pregnant women and neonates residing in the northern US are at high risk of vitamin D insufficiency, even when mothers are compliant with prenatal vitamins. Higher-dose supplementation is needed to improve maternal and neonatal vitamin D nutriture.

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Landauer's Principle that the loss of information from a computation corresponds to an increase in entropy can be expressed as a rigorous theorem of mathematical physics. However, carefully examining its detailed formulation reveals that the traditional definition identifying logically reversible computational operations with bijective transformations of the full digital state space is actually not the most general characterization, at the logical level, of the complete set of classical computational operations that can be carried out physically with asymptotically zero energy dissipation. To derive the correct set of necessary logical conditions for physical reversibility, we must take into account the effect of initial-state probabilities when applying the detailed form of the Principle. The minimal logical-level requirement for the physical reversibility of deterministic computational operations turns out to be that only the subset of initial states that are assigned nonzero probability in a given statistical operating context must be transformed one-to-one into final states. Consequently, any computational operation can be seen as conditionally reversible, relative to any sufficiently-restrictive precondition on its initial state, and the minimum average dissipation required for any deterministic operation by Landauer's Principle asymptotically approaches zero in contexts where the probability of meeting any preselected one of its suitable preconditions approaches unity. The concept of conditional reversibility facilitates much simpler designs for asymptotically thermodynamically reversible computational devices and circuits, compared to designs that are restricted to using only fully-bijective operations such as Fredkin/Toffoli type operations. Thus, this more general framework for reversible computing provides a more effective theoretical foundation to use for the design of practical reversible computing hardware than does the more restrictive traditional model of reversible logic. In this paper, we formally develop the theoretical foundations of the generalized model, and briefly survey some of its applications.