A medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health. Obesity is associated with diseases such as heart disease, type 2 diabetes, and certain types of cancer. The body mass index (BMI), which compares weight and height, is used to define a person as overweight (pre-obese: BMI = 25 kg/m2–30 kg/m2) and obese (BMI greater than 30 kg/m2).

Observational study

A study in which no experimental intervention or treatment is applied. Participants are simply observed over time. Observational studies observe, for example, what diet people have and what kind of diseases they develop.

Observational studies provide weaker evidence than a clinical trial. They can only notice associations and make suggestions (hypothesis-generating). There is a greater risk of selection bias than in intervention studies.


A disease occurring among adults that is characterized by softening of the bones due to loss of bone mineral. Osteomalacia is characteristic of vitamin D deficiency in adults, while children with vitamin D deficiency suffer from soft and deformed bones (rickets). Many of the effects of the disease overlap with the more common osteoporosis, but the two diseases are significantly different. Osteomalacia is specifically a defect in mineralization of the protein (collagen) framework.


A condition of increased bone fragility and susceptibility to bone fracture due to a loss of bone mineral density (BMD). The three main mechanisms are development of insufficient mass and strength during skeleton growth (inadequate “peak bone mass”), excessive bone depletion (resorption) and inadequate formation of new bone during “remodelling”, leading to fragile (porous) bone tissue.

Many factors increase the risk of developing osteoporosis, including being female, thin, inactive, at advanced age, and having a family history of osteoporosis. Osteoporosis is most common in women after menopause (postmenopausal osteoporosis), but may also develop in men, and may occur in anyone in the presence of particular hormonal disorders and other chronic diseases or as a result of medications.


A chemical reaction that removes electrons from an atom or molecule. The “oxidant” removes electrons from another substance, and is thus ─ as “electron acceptor” ─ itself reduced.

Oxidative stress

A condition, in which the effects of oxidizing substances (e.g. free radicalsreactive oxygen and reactive nitrogen species) exceed the ability of antioxidant systems to neutralize them.