Dietary supplements have taken a beating lately. A barrage of damning new reports suggest that millions of Americans are being bamboozled by products that are understudied, unproven, and unnecessary.

However, many researchers and physicians agree that there are three supplements men should take for optimal health. "No matter how healthy your diet, there are certain nutrients — magnesium, vitamin D, and omega-3 fatty acids — that most men lack," says Frank Lipman, an integrative physician in New York City. Deficiencies in these three particular areas can yield a whole host of health problems, studies show.

Here, why we're missing the mark on these essential nutrients, how to get enough, and what brands to trust. (We consulted with ConsumerLab, which conducts independent tests on supplements to ensure they contain exactly what the labels claim and are free of toxins.)

Magnesium: The Body's Engine
"Magnesium is the most important mineral for your body," says Dennis Goodman, a cardiologist and director of integrative medicine at New York University. "More than 350 enzymatic functions require it." Those functions regulate everything from metabolism and sleep cycles to blood pressure. With sufficient magnesium, research shows, you may help prevent problems — cardiovascular disease, type 2 diabetes, osteoporosis, and migraine headaches — and alleviate existing ones, such as muscle aches, insomnia, and anxiety.

Goodman says 70 to 80 percent of us are deficient in the mineral, even those who eat lots of leafy greens, nuts, beans, and other magnesium-rich foods. "Soils are usually depleted of magnesium, so vegetables aren't getting enough from the soil," he says.

Another all-too-common problem feeds the deficiency. "Magnesium needs go up drastically with stress," says nutritionist Andrea Rosanoff, co-author of The Magnesium Factor. When you're stressed, adrenaline spikes and blood pressure rises, and your cells consume magnesium more rapidly. "It's the difference between the gas you'd need to drive your car very slowly versus in a high-speed chase," she says. "Even with the same amount in the tank, you run out more quickly when speeding."

How Much You Need: Goodman recommends three milligrams per pound of body weight as a maintenance dose, so if you're 165 pounds, take 500 milligrams daily. (If you regularly eat lots of magnesium-rich foods, cut that dose in half.) You can take the pills any time of day, but popping them before bed may help you sleep more soundly, he adds.

Trusted Brands: Vitamin Shoppe Magnesium Citrate, Solaray Magnesium AsporotateLife Extension Magnesium (Citrate)

>>> Next, the benefits of vitamin D >>>

Vitamin D: Boost Strength, Prevent Chronic Disease
Stacks of research link vitamin D deficiency to heightened risk of heart disease, cognitive decline, and even cancer. Studies also show that getting enough of the vitamin can give immediate benefits: D bolsters your immune system to fight off infectious diseases like the flu, and because it ups the calcium you absorb from food, it helps prevent bone loss, which can begin in your thirties.

There's a modern-day reason most of us aren't getting the 2,000 IU of vitamin D many experts say we need: We shun the sun. On average, it takes 10 to 30 minutes of midday UV exposure, without wearing sunscreen, to prompt your body to generate between 10,000 and 20,000 IU of vitamin D, says Dr. John Cannell, executive director of the nonprofit Vitamin D Council. But we can fall way short of that, even in the summer. "Most of us sit at a computer all day, then walk to and from our cars when the sun is too low to produce UV," says Robert Heaney, an endocrinologist at Creighton University. "It doesn't matter where you live. We've evaluated vitamin D statuses of hospital workers in Hawaii and Alaska, and they're exactly the same." Compounding this deficiency problem is the fact that, as you age, your body becomes less efficient at synthesizing the vitamin. According to a report from the Berkeley School of Medicine, a 70-year-old man synthesizes only about a quarter as much vitamin D as a 20-year-old who gets the same sun exposure.

You can't count on food, either. "Even vitamin D–fortified eggs and milk are basically useless," Cannell says. "You would have to drink 50 glasses of milk per day to get enough."

How Much You Need: "As a rule of thumb, get 30 to 35 IU per pound of body weight per day," Heaney says. (So again, if you're 165 pounds, that's about 5,000 IU.) Downing megadoses won't give you more benefit, and it may cause calcium buildup in the blood vessels, cautions JoAnn Manson, an epidemiology professor at the Harvard School of Public Health.

Make sure you buy vitamin D3, not D2. D3 is what you'd make from the sun, while D2 is synthetic and takes longer to convert to a usable nutrient in the body, Heaney says. That means you need higher doses and have to take it more often to get the benefits, he says. Finally, take the pill with a meal. Vitamin D is fat soluble, says Dr. Tod Cooperman, president of ConsumerLab, and you may absorb up to 50 percent more if you pair it with food.

Trusted Brands: Nature Made Vitamin D 2,000 IU, Source Naturals Vitamin D3, Simply Right Vitamin D3.

>>> Next, why you should be taking fish oil >>>

Fish Oil: Sharpen Your Mind
You've probably seen recent headlines claiming that fish oil supplements may not help to protect your heart. Dig into the research, though, and you'll see that some small studies show that fish oil doesn't help those with heart disease — but doctors and researchers alike still believe that omega-3-rich supplements keep the hearts of otherwise healthy men in good shape, possibly preventing heart attacks. "We know that omega-3s, such as DHA and EPA found in fish oil, lower triglycerides, reduce inflammation, stabilize heart rhythms, and, at higher intakes, help prevent blood clotting," Manson says.

Aside from heart-health benefits, fish oil, she adds, may also sharpen brain function, boost mood, and reduce depression. Several studies suggest it could even help stave off Alzheimer's disease. What's more, Manson says, "because of its anti-inflammatory effects, fish oil may help ease muscle and joint aches and make skin look younger."

If you're not eating fatty fish like salmon and mackerel two or three times a week, Lipman says it's safe to assume you're deficient in omega-3s. "Fish oil is an easy way to make up for them," he says.

How Much You Need: Aim to get one to three grams of DHA and EPA per day, taken any time of day. Capsule sizes vary, and liquid fish oil tends to be more potent, so be vigilant about label-reading, because there is a small risk of internal bleeding if you go above four grams per day.

Trusted Brands: Kirkland Signature Natural Fish Oil 1000, Nordic Naturals Ultimate Omega, the Vitamin Shoppe Omega 3 Fish Oil (liquid).