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UNSW scientists have identified a molecular switch in the body that regulates production of two substances vital to human health – cholesterol and vitamin D.

They have shown that when levels of cholesterol are high, the switch is flicked so that less cholesterol is made and more vitamin D is produced in the skin.

The researchers say it is important to understand the processes that control production of these two vital substances and ensure a balance is maintained, to inform future medical recommendations.

“Too much cholesterol can lead to heart disease,” says lead author Anika Prabhu, of the UNSW School of Biotechnology and Biomolecular Sciences.

“On the other hand, vitamin D deficiency has been associated with an increased risk of several conditions, including osteoporosis, autoimmune disease and diabetes.

“More and more individuals are being diagnosed with vitamin D deficiency and taking supplements. So it is particularly important that we develop a better understanding of the control of vitamin D levels in the body, as well as levels of cholesterol," she says.

The study by Professor Andrew Brown’s lab at UNSW is published in the Journal of Biological Chemistry.

Cholesterol, which is essential for cell growth, is produced in the body by a complex series of reactions involving more than 20 different steps.  The last step relies on the enzyme DHCR7, which converts a substance called 7DHC into cholesterol.

This substance, 7DHC, can also be turned into vitamin D by UV from sunlight.

The UNSW team showed in cell culture experiments that high levels of cholesterol destroyed the enzyme, switching off cholesterol production. This led to a build-up of 7DHC, which increased production of vitamin D in skin cells exposed to UV.

“Our study is the first to show this very interesting relationship between these two crucial molecules – cholesterol and vitamin D,” says Professor Brown.

In a rare number of cases, babies who have a defective DHCR7 enzyme produce no cholesterol and develop a devastating developmental disorder called Smith-Lemli-Opitz syndrome.

In the same laboratory study, the UNSW researchers showed that treatment with the cholesterol-lowering drugs statins might be a possible way to overcome the lack of activity of the enzyme in this disease. The study highlights the sophisticated ways our bodies carefully balance cholesterol and vitamin D levels to ensure good health.