essential nutrients

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Vitamin D
Long underestimated, vitamin D is much more than just a bone fortifier; there's strong evidence that adequate levels can reduce our risk for many cancers, says Willett, and can protect against heart disease and type 2 diabetes. One study found that people with very low levels of vitamin D in their blood are 26 percent more likely to die from any cause (heart disease, cancer, infection, etc.) than those with recommended amounts. The challenge is that very few foods in nature contain vitamin D.

You need: 600 IU a day; 800 IU if over 80.

You get: Willett says that about half of Americans, and 80 percent of those with darker skin, don't get enough (higher amounts of melanin in the skin interfere with vitamin D absorption).

Good sources: The easiest way to get vitamin D used to be from the sun, but now our risk of skin cancer is high enough that all dermatologists (and most nutritionists, including Willett) advise instead to rely on food or supplements. Your best bet is the flesh of fatty fish (such as salmon, tuna and mackerel). A tablespoon of cod liver oil has 340 times the RDA (though many folks cannot stomach it). Smaller amounts are naturally found in beef liver, cheese and egg yolks. You can also find vitamin D in fortified milk, yogurt and orange juice . (Talk to your doctor about supplements).
As a reminder, always consult your doctor for medical advice and treatment before starting any program.