Why You Need It: You know calcium helps build strong bones, but it’s also necessary for the secretion of hormones and enzymes, proper nervous-system function, muscle contraction, and the contraction and expansion of blood vessels.
Low Blood Calcium Levels: Our bodies pull calcium from bone tissue, which over time can lead to low bone mass (osteopenia) and porous, fragile bones (osteoporosis). Calcium is best absorbed in doses of less than 500 mg, so divide your supplemental intake into two doses per day. If you experience gas, bloating or other undesirable side effects, take it with food.
Best Food Sources: Calcium-fortified orange juice, canned salmon with bones, dairy products, sardines canned in oil with bones.
Best Supplement Sources: Calcium citrate (take anytime), calcium carbonate (take with meals).

Why You Need It: This micronutrient plays a role in more than 300 reactions in the body, as well as contributes to muscle and nerve function, a healthy immune system, bone strength, blood pressure, energy metabolism and protein synthesis.
Low Magnesium Levels: Sufficient body stores of magnesium can protect against cardiovascular disease and immune dysfunction. Although cases of extreme magnesium deficiency are rare in the U.S., it can lead to many side effects.
Best Food Sources: Baked potatoes, black-eyed peas, dry-roasted almonds and cashews, halibut, mixed nuts, peanuts and peanut butter, plain yogurt, soybeans, spinach.
Best Supplement Sources: Oxide, sulfate, carbonate (Citracal Plus with vitamin D and magnesium, and Slow- Mag with calcium and magnesium).
Why You Need It: Vitamin D promotes calcium absorption, incorporates calcium into bone tissue, maintains bone strength, and is necessary for immune and neuromuscular function.
Low Vitamin D Levels: This deficiency can contribute to the softening of bones, muscle and bone pain, and possible decreased immune system function.
Best Food Sources: Cooked salmon or mackerel, fortified milk and orange juice, Monterey mushrooms (enriched with vitamin D), sardines or tuna canned in oil, yogurt.
Best Supplement Sources: Vitamin D3 (cholecalciferol).