VITAMIN A

What it does
Promotes good eyesight and has the same immunity-boosting properties as vitamin C.
Should you supplement?
Most guys get enough from food, and taking a pill could result in an overdose of A, which could lead to liver damage. But if you've been catching colds more frequently or if your eyesight seems weaker, try cod-liver oil—it's what ancient mariners used to boost night vision.
Best food sources
Liver from chicken, beef, and pork, sweet potatoes, spinach, cantaloupes, carrots, kale, collard greens.

VITAMIN B

What it does
This family of eight vitamins enhances energy levels, regulates mood, and boosts your immune system.
Should you supplement?
They often come together in a B-complex, along with claims that they cure wrinkles, fight muscle fatigue, and relieve hangovers—none of which are backed by science. More to the point, men should avoid B-complex vitamins because it's easy to get too much of B9, which has been linked to prostate cancer. The exception is for vegetarians, who should take B12.
Best food sources
Chicken, eggs, turkey, tuna, salmon, beef, lentils, peas, Swiss chard, spinach, black beans.

VITAMIN C

What it does
Also known as ascorbic acid, C helps fight skin aging and keeps your tendons and ligaments young, preventing injury. And it's your immune system's bestie.
Should you supplement?
The daily recommended intake is 90mg, but if you're skimping on sleep and excessively working (or working out), you should pop 250 to 500mg daily. If Vitamin C gives you heartburn, take the low-acid buffered version.
Best food sources
Broccoli, Brussels sprouts, oranges, grapefruits, tomatoes, chili peppers, kale, strawberries.

VITAMIN D

What it does
Protects against depression, cancer, and heart disease. Symptoms of deficiency include fatigue and depression. If that sounds like you, ask your doctor for a summer and winter test to see how your levels fluctuate with the amount of sunlight you get.
Should you supplement?
A deficiency is bad for your body, but taking a D supplement can be worse—the pill form of the vitamin has been linked to prostate and pancreatic cancers in men. Instead, watch your weight (losing 5 to 10 percent of your body weight can increase levels by 34 percent), eat more D-rich foods, and get more sun.
Best food sources
Salmon, sardines, cheese, eggs, mushrooms.

VITAMIN E

What it does
Promotes healthy skin, protects against bladder and prostate cancers, and is vital for brain health.
Should you supplement?
Pop an E and you can amp up your sperm count and reverse aging, according to manufacturers' claims—which aren't backed by science. In fact, some studies link the supplement to lung cancer.
Best food sources
Eggs, sunflower seeds, almonds, olives, spinach, Swiss chard, turnip greens, whole grains.