**12. Oligoelements in water**

Epidemiological studies have revealed both a higher incidence of CVDs and cerebrovascular mortality in soft water areas and a negative correlation between water hardness and cardio‐ vascular mortality [56,57]. Actually, there is not enough evidence to determine whether hard water contains protective substances not present in soft water or if there are detrimental substances in soft water*.*

Water contains oligominerals, such as calcium, magnesium, cobalt, lithium, vanadium, sili‐ con, copper, iron, zinc and manganese, that are some important factors in reducing the risk of CVD onset. On the other hand, elements like cadmium, lead, silver, mercury and thallium are considered to be harmful [58].

Magnesium deficiency is considered to be a risk factor of CVDs, in fact its supplementation delays the onset of atherosclerosis or hinders its development. On the other hand, silicon is a major trace element in animal diets and humans ingest between 20-50 mg/day of silicon with the Western diet [59]. Main dietary sources are whole grain cereals and their products (including beer), rice, some fruits and vegetables and drinking water, especially bottled min‐ eral waters with geothermal and volcanic origin [60]. Numerous studies showed that silicon has a role in maintaining the integrity, the stability and the elastic properties of arterial walls [61,62] and postulated silicon as a protective factor against the development of age-linked vascular diseases, such as atherosclerosis and hypertension [62,63].

In addition, vanadium is considered to have anti-atherosclerotic properties; lithium can also inhibit the synthesis of cholesterol, but has an atherogenous activity that can be inhibited by supplementation with appropriate quantities of calcium. A copper-deficient diet can induce hypercholesterolemia and hypertriglyceridemia that is, in turn, intensified by high levels of dietary zinc [58,64].

On the basis of these limited data, intakes of silicon, magnesium and vanadium in water and avoiding exposure to cadmium and lead are important elements of the prophylaxis of CVDs, so hard water has positive health effects and should not be replaced by drinking wa‐ ter with insufficient amounts of beneficial elements [58]. It is important to remember also that water has small contribution of mineral trace respect to total dietary intake (7% from liquid vs 93% from solid food) [58,65].
