336 OLIVE OILS AND HEALTH Pregnant women, older adults, individuals with darker skin, and those with insufficient sun exposure are at increased risk of vitamin D deficiency. It is important to note that sun exposure should be approached with caution, as excessive exposure can lead to skin cancer. Deficiency may also occur in individuals with malabsorption disorders (coeliac disease, etc.), those taking medications that affect vitamin D metabolism, those who are overweight, or those with kidney failure. Long-term vitamin D deficiency can lead to a loss of bone density, increasing the risk of osteoporosis and fractures. In children, severe deficiency can cause rickets (in which the bones become soft, weak, deformed, and painful). In adults, severe deficiency leads to osteomalacia (weak bones, bone pain, and muscle weakness). Vitamin D supplementation has been proposed for the prevention of various diseases such as cancer, osteoporosis, psoriasis, etc. However, further research is needed to determine whether vitamin D supplementation can reduce the risk of developing these conditions. So far, its efficacy has only been clearly demonstrated in the treatment of existing vitamin D deficiencies, such as in cases of rickets. VITAMIN E (See MINOR COMPOUNDS / Tocopherols) VITAMIN K Vitamin K is a fat-soluble vitamin (soluble in fats and organic solvents). It exists in two natural forms: K1, also called phylloquinone or phytomenadione, and K2 or menaquinone, which is more biologically active. The body can convert vitamin K1 into K2. In addition to these natural forms, there are also three synthetic types: K3 (menadione), K4 and K5. The body stores vitamin K in the liver and in other tissues such as the brain, heart, pancreas, and bones. Vitamin K contributes to blood clotting and is also involved in bone formation. Dietary sources of K1 include mainly green leafy vegetables such as spinach, cabbage, broccoli, and lettuce. It is also found in some fruits (e.g., blueberries, figs) and in some oils such as soy or canola. K2 is present in animal-derived products and fermented foods such as cheese and sauerkraut (fermented cabbage). Although certain gut bacteria in the intestinal microbiota can produce small amounts of K2, dietary intake is still necessary. Vitamin K is usually easy to obtain through a varied and balanced diet, and supplementation is generally not needed unless a deficiency is diagnosed. While a single high dose is not associated with adverse effects, long-term excessive use, particularly of synthetic forms, may pose health risks. Recommended intake levels vary with age and between sources. As a general guide: infants under 12 months need around 2-2.5 micrograms (µg)/day; children and adolescents aged 1-18 years require 30-60 µg/day; and adults need between 50 and 120 µg/day. Vitamin K deficiency is uncommon in healthy adults because many green vegetables contain it, and because small amounts are also produced by intestinal bacteria. Nevertheless, severe vitamin K deficiency can lead to bruising and bleeding problems due to impaired blood clotting. It may also weaken bones and increase the risk of osteoporosis, as vitamin K plays also a role in bone health. Deficiency can be corrected with vitamin K supplements taken orally or administered via subcutaneous injection. Individuals on anticoagulant treatment should avoid consuming foods that are high in vitamin K, as it may interfere with the medication’s effectiveness. Infants up to around 6 months of age
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