Scientists continue to try and recreate aspects of the biochemical changes brought on by calorie restriction, in an effort to generate the health and longevity benefits via medicine. An example can be found at ScienceDaily: "a newly discovered vitamin activates the yeast anti-aging gene product Sir2, which resembles sirtuins found in humans. ... NR (nicotinamide riboside), a natural product found in milk. Like the B3 vitamin, niacin, NR is a precursor to a versatile cellular factor that is vital for all life. The factor, called NAD, short for nicotinamide adenine dinucleotide, is elevated by calorie restriction. So the researchers set out to develop an intervention to elevate NAD, using yeast cells, whose genes are easy to manipulate. ... It's surprising that no one was be able to elevate NAD with a small molecule before ... The team discovered two pathways that allow yeast to raise NAD levels with NR, improve their control of gene expression and live longer in the presence of high glucose." Some folk in the gerontology community are skeptical, pointing out that no success has been obtained in mammals through the use of other precursor biochemicals in this pathway - this may be one of the many differences rather than similarities between yeast and people.