Why You Need It: Not only does D help the body absorb calcium, it also might play a role in preventing colon cancer, breast cancer and diabetes.
Daily Dose: 2,000 international units (IUs) of vitamin D-3 in the winter. In summer, drop down to 1,000 IUs or skip it on days you get lots of sun. Omega-3 Fatty Acids
Why You Need It: Low levels of these healthy fats can lead to internal inflammation, one culprit behind heart disease, diabetes and cancer.
Daily Dose: 1 to 2 grams (1,000 to 2,000 mg). Take fish-oil supplements with food, which absorbs the oil and staves off fishy burps.
Why You Need It: Probiotics, or good bacteria, have been shown to assuage gastrointestinal problems, like diarrhea, and even help reduce colds.
Daily Dose: One capsule with 10 billion colony-forming units (CFUs), preferably in the morning so it can aid your digestion throughout the day.
Sources: Christine Gerbstadt, MD, author of Doctor's Detox Diet: The Ultimate Weight Loss Prescription; and David Katz, MD, director of the Yale-Griffin Prevention Research Center and author of Disease Proof Source