Between 70% and 90% of common cancers are due to environmental factors and therefore potentially preventable.Greater than 30% of cancer deaths could be prevented by avoiding risk factors including: tobacco, excess weight/obesity, poor diet, physical inactivity, alcohol, sexually transmitted infections and air pollution. Further, poverty could be considered as an indirect risk factor in human cancers. Not all environmental causes are controllable, such as naturally occurring background radiation and cancers caused through hereditary genetic disorders and thus are not preventable via personal behavior. Dietary
While many dietary recommendations have been proposed to reduce cancer risks, the evidence to support them is not definitive. The primary dietary factors that increase risk are obesity and alcohol consumption. Diets low in fruits and vegetables and high in red meat have been implicated but reviews and meta-analyses do not come to a consistent conclusion. A 2014 meta-analysis found no relationship between fruits and vegetables and cancer. Coffee is associated with a reduced risk of liver cancer. Studies have linked excessive consumption of red or processed meat to an increased risk of breast cancer, colon cancer and pancreatic cancer, a phenomenon that could be due to the presence of carcinogens in meats cooked at high temperatures.
Hedgehog proteins are also involved in the transcription of genes that regulate cell proliferation and differentiation. Cholesterol is important to this pathway because it undergoes covalent bonding to Hedgehog proteins, resulting in their activation. Without cholesterol, the signaling activity is disrupted and cell differentiation may be impaired.Cholesterol is a precursor for many important molecules. These include bile acids (important in processing dietary fats), oxysterols, neurosteroids (involved in neurotransmission and excitation), glucocorticoids (involved in immune and inflammatory processes), mineralocorticoids (osmotic balance), and sex steroids (i.e. estrogen and testosterone; wide range of function but involved in genital development prenatally). Finally, cholesterol is a major component of myelin, a protective layer around neurons. Myelination occurs most rapidly during prenatal development, meaning that the demand for cholesterol biosynthesis is very high. Pathogenesis
Given that the function of cholesterol encompasses a very wide range, it is unlikely that the symptoms of SLOS are due to a single molecular mechanism. Some of the molecular effects are yet unknown, but could be extrapolated based on the role of cholesterol. In general, the negative effects are due to decreased levels of cholesterol and increased levels of cholesterol precursors-most notably, 7DHC. Although 7DHC is structurally similar to cholesterol, and could potentially act as a substitute, the effects of this are still being studied.Most patients with SLOS present decreased cholesterol levels, particularly in the brain (where cholesterol levels rely primarily on new synthesis). This also means that any sterol derivatives of cholesterol would also have reduced concentrations.