These six key nutrients can keep you healthy

Although mainstream today, the idea that women have different nutritional needs than men isn't as old as you might think. "The field of women's nutrition has only been around for a few decades," says Ann Yelmokas McDermott, Ph.D., M.S., L.N., nutrition scientist at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston. Fifty years ago, proper nutrition―for everyone―simply meant three solid meals each day.

"Every year, there's more promising research revealing how nutrients can have a significant positive impact on disease prevention and general well-being in women," McDermott says. "That's great news, because changing your diet is one of the simplest ways to improve your health." With the help of the American Dietetic Association (ADA), we've identified six of the nutrients that women need most. Making sure that you include them as part of a well-balanced diet will help ensure that you become―and stay―your healthiest.

1. Folic Acid

What it is: "Folic acid" and "folate" are often used interchangeably, but they are not exactly the same. Folic acid is the synthetic form of this B vitamin found in multivitamins and fortified foods, while folate is the type found naturally in food.

What it does: "Given that about 50 percent of pregnancies in the United States are unplanned, all women of reproductive age should make an effort to get enough folic acid," says Susan Moores, R.D., a nutrition consultant in Minneapolis and ADA spokesperson. Low levels of folic acid in expectant mothers can cause neural-tube birth defects in their children. Perimenopausal and postmenopausal women can benefit from the vitamin, too. "It's crucial for the creation of new cells, and for the creation and maintenance of dna; it may even have anti-cancer properties, although the research on that is divided," Moores says. Folic acid also lowers levels of homocysteine, an amino acid in the blood that has been linked to dementia, cognitive impairment, stroke, and heart disease. Preliminary research also suggests that optimal intakes may help prevent depression.

How much you need: A minimum of 400 micrograms (mcg) per day

Where to find it: Folic acid is found in fortified breads, cereals and pastas, and in multivitamins. Food sources of folate include dark, leafy greens like spinach and kale; nuts; and legumes. Oral contraceptives, antacids, and some medications used to treat type 2 diabetes may inhibit folic acid absorption, so women taking them may need to increase their intake. Talk to your doctor to find out more.

2. Calcium

What it is: Calcium is the most abundant mineral in the human body. It forms the basic architecture for bones and teeth.

What it does: "Calcium has been shown to promote bone growth and prevent osteoporosis, or bone loss, which affects millions of women in the United States," Moores says. But other benefits of the mineral are less widely recognized. Preliminary research suggests that calcium may play a role in preventing breast cancer, although researchers aren't sure why. A 2005 study from the American Cancer Society reported that postmenopausal women who consumed more than 1,250 milligrams (mg) of calcium per day were 20 percent less likely to develop breast cancer than women who consumed less than 500mg daily. Additionally, a 2005 study from the University of Massachusetts, Amherst, found that women with a diet high in both calcium and vitamin D (a nutrient crucial for calcium absorption) were less likely to experience premenstrual syndrome.

How much you need: Before menopause, women need 1,000mg calcium per day. After, the recommendation rises to 1,200mg to help offset bone loss that occurs with age. Because the body can only digest so much calcium at one time, divide your dose, consuming no more than 500mg per sitting.

Where to find it: Calcium-rich foods such as low-fat dairy products, almonds, and some greens, including kale and broccoli, are the best sources of calcium, but supplements also can help you meet your daily requirement. "Calcium citrate is more easily absorbed than calcium carbonate, particularly if taken on an empty stomach," Moores says.

3. Vitamin D

What it is: Although it's classified as a vitamin, vitamin D actually works more like a hormone in your body. When it's converted into its most biologically active form―calciferol―by the liver and kidneys, it helps the intestines absorb more calcium from food. That's why you often find calcium-rich foods fortified with vitamin D.

What it does: Because vitamin D helps your body absorb calcium, it's crucial for preventing osteoporosis. Though it's a great reason for making sure you get enough, it's not the only reason you need it. "New research shows that vitamin D may play a role in preventing several types of cancer," McDermott says. Earlier this year, a review of 63 studies conducted by the University of California at San Diego suggested that increasing vitamin D intake may help reduce the incidence of breast, colon, and ovarian cancers. One theory, says McDermott, is that adequate vitamin D helps cells develop normally instead of becoming damaged and cancerous.

How much you need: According to McDermott, the current daily vitamin D recommendations of 200 International Units (IU) for adults ages 19 to 50 and 400 IU for those 51 to 70 appear to be insufficient. "Dietary guidelines don't take into account new research from the past seven years, which suggests that higher doses may be optimal," she says. "Expect daily vitamin D recommendations to increase significantly in the next few years." In the meantime, McDermott recommends that adult women aim for at least 400 IU a day. If you're 51 or older, aim for 600 IU.

Where to find it: Vitamin D is naturally found in oily fish like anchovies and salmon and in fish and cod liver oil supplements. Many dairy products like milk, and even some cereals, are fortified with it. A cup of milk should contain 100 IU of vitamin D. It's also found in multivitamins and supplements. Since the vitamin is fat-soluble (meaning that it cannot be digested without the aid of dietary fat), be sure to take it with food. Vitamin D is one of the few nutrients our bodies make naturally; it's produced by the skin as a result of exposure to the sun's UVB rays. "That's not a license to tan, but spending 10 to 15 minutes in the sun a few times a week, without sunblock, is a good idea," McDermott says. "That amount of time will supply all the vitamin D you need."

4. Iron

What it is: The mineral that helps the body's blood supply deliver oxygen to cells. What it does: Almost two-thirds of the body's iron supply is found in hemoglobin, the protein in red blood cells that carries oxygen to tissues. For that reason, iron is key to maintaining energy levels. According to the ADA, women report fatigue three times more often than men, and it can be directly linked to low levels of iron. Consistently low levels of iron can cause anemia, a condition experienced by three to five percent of American women.

How much you need: Postmenopausal women need 8mg iron per day, while women of child-bearing age and nursing mothers require 18mg. "When a woman is menstruating, there's a blood loss, so iron levels are lower," McDermott says. During reproductive years, women are at an increased risk for iron deficiency because they lose 20 to 40mg iron each month during menstruation. During pregnancy, the recommended daily amount increases to 27mg due to increased blood volume and the needs of the developing child.

Where to find it: There are two forms of iron: heme iron, found in animal foods such as red meat, fish, and poultry; and non-heme iron, found in plant foods such as beans and spinach. The body uses 15 to 35 percent of the heme iron obtained from diet. Only 2 to 20 percent of non-heme iron is absorbed from food. "To help increase absorption, eat food sources of non-heme iron along with foods that contain high levels of vitamin C, such as tomatoes, bell peppers, and citrus fruits," says Dawn Jackson Blatner, R.D., a nutrition counselor at Northwestern Memorial Hospital Wellness Institute in Chicago and ADA spokesperson.

5. Fiber

What it is: There are two types of fiber-soluble and insoluble. Because both kinds are passed through the body rather than being absorbed into it, not all experts agree that fiber qualifies as a nutrient, per se. But they do agree on its importance in the diet.

What it does: Unlike folic acid, the benefits of fiber aren't unique to female physiology. Its functions apply equally to men and women. "Soluble fiber traps 'bad' cholesterol before it's absorbed by your intestines, which helps reduce the risk of heart disease, the number-one killer of American women and men," Blatner says. "Insoluble fiber sweeps through your system, cleaning out your digestive track." Fiber-rich foods also help with two common concerns for many women―energy and weight control. "Fibrous foods are filling, yet don't contain a lot of calories," Blatner says. "They keep you from feeling hungry, and because fiber helps your body digest food more slowly than it normally would, they sustain energy levels for long periods of time."

How much you need: Aim for 30 grams (g) of fiber per day divided into three segments: 10g at breakfast, 10g at lunch, and 10g at dinner. If you eat little fiber now, start slowly, with around 15g per day, working your way up to 30g over the course of a month; stocking up suddenly can lead to digestive problems, like cramping and constipation.

Where to find it: Food sources of fiber contain both soluble and insoluble. Look for instant or slow-cooked oatmeal; whole-grain bread and pasta (remember to check the label closely―look for the word "whole"―enriched wheat or multigrain aren't the same thing as whole-grain); popcorn; fruits, including apples and berries; vegetables like peas and broccoli; and beans, which can contain up to 10 grams of fiber in a serving.

6. Omega-3 Fatty Acids

What it is: Omega-3 fatty acids, a form of polyunsaturated fat, are one of the "good" fats. They're part of a group of essential fatty acids, so-called because the body cannot convert other types of fat molecules into the omega-3 form; they can only be supplied by diet.

What it does: Like fiber, omega-3's benefits are universal. "Eating three ounces of omega 3-rich fish two to three times a week can reduce stroke risk by up to 60 percent in women," says Leslie Bonci, R.D., M.P.H., director of sports medicine nutrition at the University of Pittsburgh Medical Center. "Omega-3 fatty acids decrease triglycerides (aka blood fats), boost good hdl cholesterol, and decrease blood pressure-all of which can lower the risk of cardiovascular disease." What's more, studies show that omega-3s function as anti-inflammatory agents, reducing the cellular inflammation that can worsen conditions from arthritis to heart disease.

How much you need: 1.1g per day

Where to find them: Fish are the best source. Wild salmon, halibut, non-white tuna, sardines, herring, and anchovies are high in omega-3s and low in mercury, a neurotoxin fish obtain from polluted water or by eating other fish that contain high levels of it. Dietary supplements are also an option; choose fish oil capsules that are labeled "distilled" to obtain the purest form of omega-3s, Bonci says.

Camille Noe Pagán writes about health, psychology, and nutrition for magazines, including Glamour and Health.