 Fluoride can be present naturally in water at concentrations well above recommended levels, which can have several long-term adverse effects, including severe dental fluorosis, skeletal fluorosis, and weakened bones.In 1984 the World Health Organization recommended a guideline maximum fluoride value of 1.5 mg/L as a level at which fluorosis should be minimal, reaffirming it in 2006.Fluoridation has little effect on risk of bone fracture (broken bones); it may result in slightly lower fracture risk than either excessively high levels of fluoridation or no fluoridation.