You may have heard that breast milk is best. But what makes it so good for babies? Breast milk fills your baby’s health needs. Researchers are now learning more about what’s in it and how it changes as babies grow.

“Breastfeeding is the gold standard for feeding infants,” says Dr. Dan Raiten, an NIH expert on childhood nutrition. Human milk provides nutrients and other compounds that babies need to grow and develop. These include proteins, fats, carbohydrates, vitamins, and minerals.

Experts recommend that infants drink human milk exclusively for the first six months of life. If possible, they should continue drinking human milk, from the breast or that’s been pumped and placed in a bottle, for up to 12 months. Parents can add in other foods starting around six months.

Breastfeeding (sometimes called chestfeeding) lowers an infant’s risk for developing asthma, obesity, type 1 diabetes, ear infections, gut infections that cause diarrhea or vomiting, and sudden infant death syndrome (SIDS). It also benefits the mother, potentially lowering her risk of high blood pressure, type 2 diabetes, ovarian cancer, and breast cancer. It helps the parent-infant bonding process, too.

Human milk also provides infants with protection from germs. A baby’s immune system is not yet developed. So they don’t have many germ-fighting molecules, called antibodies. Breast milk passes the mother’s antibodies to the baby. This helps protect the child from germs until their immune system develops.

Breast milk contains many other biologically active components, too. “Human milk is not just a composite of individual components,” Raiten says. “It’s an active biological system.” The lactating (milk-producing) parent and infant interact and affect one another. That means what’s in human milk can change, even over the course of the day.

Take the molecules that regulate your body’s biological clocks, or circadian clocks. Your body has different amounts of these depending on the time of day. They signal when it’s time to wake, eat, and sleep. These are passed along to the baby through breast milk.

Researchers are just beginning to understand how milk composition affects babies’ short-term and long-term health. To learn more, NIH started the BEGIN project. This project is trying to untangle the biology behind milk production, how milk affects babies’ development, and how babies and their environment influence this system.

Some lactating parents don’t produce enough milk or may have physical issues that block milk from coming out. Others may be advised against breastfeeding if they’re taking certain medications or drugs or when they have certain illnesses.

For those who can’t breastfeed, formula is an option. “Formula is based on our best knowledge about the composition of human milk,” Raiten says. And that knowledge continues to evolve.

“If you can do it, breastfeeding is the best way to take care of your baby,” says Raiten. If you’re having trouble, talk with your health care provider.

Getting Started Breastfeeding

• Cuddle with your baby skin-to-skin right after giving birth if you are both healthy.
• Breastfeed as soon as possible after giving birth.
• Ask for a lactation consultant at the hospital to help you.
• Ask hospital staff not to give your baby pacifiers, sugar water, or formula, unless medically necessary.
• Let your baby stay in your hospital room all day and night so that you can breastfeed often.
• Try not to give your baby any pacifiers or artificial nipples until they’re good at latching on to the breast (usually 3 to 4 weeks old).
• Learn your baby’s hunger signs. They may become more alert and active. They may put their hands or fists to their mouth, make sucking motions, look around for the breast, or cry.

The U.S. Dietary Guidelines for Americans recommend that infants be exclusively breastfed for about the first 6 months, and then continuing breastfeeding while introducing appropriate complementary foods until your child is 12 months old or older. The American Academy of Pediatrics and the World Health Organization also recommend exclusive breastfeeding for about the first 6 months, with continued breastfeeding along with introducing appropriate complementary foods for up to 2 years of age or longer.

Vitamins & Minerals

Breastfed babies need additional vitamin D and may need additional iron. Although breast milk is an excellent source of the nutrition your baby needs, he or she will need to get extra vitamin D (beginning at birth) and possibly iron from supplements.

Benefits

Breastfeeding is good for both you and your baby. Breast milk is the best source of nutrition for most babies. As your baby grows, your breast milk will change to meet his or her nutritional needs. Breastfeeding can also help protect you and your baby against some short- and long-term illnesses and diseases.

Micronutrient deficiencies can have devastating consequences. Micronutrients, also called vitamins and minerals, are key to helping fetuses, infants, and children grow and thrive. Facts about six essential nutrients are outlined here.

Iodine is a vital component of thyroid hormones thyroxine (T4) and triiodothyronine (T3). The mother’s thyroid hormone levels affect proper fetal growth and neurological development during pregnancy and after birth.

Who is at risk for iodine deficiency while breastfeeding?

• Women who do not regularly consume dairy products or seafood.
• Women who smoke cigarettes.
• Women who do not use iodized salt.
• Women who eat foods containing goitrogens, which are substances that can affect how well
  the thyroid gland makes thyroid hormones. These foods include brussel sprouts, kale, cabbage, cauliflower, radishes, and broccoli.

Do infants get enough iodine from breast milk?

Usually. The recommended dietary allowance (RDA) (the average amount of a vitamin or mineral that meets the daily nutrient needs of nearly all healthy people) of iodine is higher for women when they are pregnant or breastfeeding in order to support proper fetal or infant growth and neurological development. Although breast milk contains iodine, concentrations can vary based on maternal iodine levels. If a pregnant or breastfeeding woman is deficient in iodine, the fetus or infant may be at risk for iodine deficiency and associated cognitive and psychomotor impairments.

Because the diet of a pregnant or breastfeeding woman may not contain enough iodine to meet the RDA, the American Thyroid Association and the American Academy of Pediatrics recommend that pregnant or breastfeeding women take a daily multivitamin or prenatal supplement every day containing 150 µg of iodine.

Not all multivitamin and prenatal supplements contain 150 µg of iodine; therefore, all women should check the nutrition label or speak with their health care provider about whether their multivitamin supplement or prenatal vitamin contains enough iodine.

Iron is necessary to make hemoglobin, which carries oxygen in red blood cells to all parts of the body. Iron also supports proper neurological development during infancy and early childhood.

Do infants get enough iron from breast milk?

Most newborns have sufficient iron stored in their bodies for about the first 6 months of life depending on gestational age, maternal iron status, and timing of umbilical cord clamping. By age 6 months, however, infants require an external source of iron apart from breast milk. Breast milk contains little iron; therefore, parents of infants receiving only breast milk should talk to their infant’s health care provider about whether their infant needs iron supplements before 6 months of age.

If an infant is receiving only iron-fortified infant formula (during the time before complementary foods are given), then additional iron supplementation is not necessary.

At about 6 months of age, an infant’s iron needs can be met through the introduction of iron-rich foods, iron-fortified cereals, or iron supplement drops.

Infants need vitamin B12 for supporting brain development and producing healthy red blood cells. Infants who do not get adequate vitamin B12 can become deficient. If left untreated, vitamin B12 deficiency in infants can lead to permanent brain damage. Vitamin B12 is found in foods from animals, primarily meat, fish, milk and milk products, and eggs; therefore infants of mothers who consume a vegetarian or vegan diet may be at risk for vitamin B12 deficiency.

Do infants get enough B12 from breast milk?

Usually. Vitamin B12 is transferred through the placenta to the fetus during pregnancy and through breast milk after birth. Infants who drink breast milk from a mother who consumes adequate amounts of vitamin B12 or infants who drink infant formula, will receive enough vitamin B12. However, if a breastfeeding mother is deficient in vitamin B12, her infant may also become deficient.

Vitamin B12 is most commonly found in foods from animals; therefore, infants who only receive breast milk from mothers who consume no animal products are at greater risk for developing vitamin B12 deficiency shortly after birth. Breastfeeding mothers on a strict vegetarian or vegan diet should consult their healthcare provider about taking a supplement that contains the appropriate amount of vitamin B12.

Breastfeeding mothers who have had a malabsorptive bariatric procedure (such as gastric bypass surgery), who have pernicious anemia (low number of red blood cells caused by a deficiency of vitamin B12), or who have certain gastrointestinal disorders, may not be able to absorb various vitamins and minerals, such as vitamin B12, folic acid (vitamin B9), iron, and calcium. Healthcare providers should monitor these mothers for nutrient deficiencies, including vitamin B12 deficiency.

Vitamin D is needed to support healthy bone development and to prevent rickets, a condition that causes weak or deformed bones. Vitamin D deficiency rickets among breastfed infants is rare, but it can occur if an infant does not receive additional vitamin D from foods, a vitamin D supplement, or adequate exposure to sunlight.

Do infants get enough vitamin D from breast milk?

Breast milk alone does not provide infants with an adequate amount of vitamin D. Shortly after birth, most infants will need an additional source of vitamin D.

To avoid developing a vitamin D deficiency, the Dietary Guidelines for Americans and American Academy of Pediatrics recommend breastfed and partially breastfed infants be supplemented with 400 IU per day of vitamin D beginning in the first few days of life. Families who do not wish to provide a supplement directly to their infant should discuss with a healthcare provider the risks and benefits of maternal high dose supplementation options.

Once a child has started eating solid foods, parents can make sure their child is getting enough vitamin D from foods or supplements.

Why are infants at risk for vitamin D deficiency?

The risk for vitamin D deficiency is increased when there is limited exposure to sunlight or when an infant is not consuming an adequate amount of vitamin D. Although reducing sun exposure is important for preventing cancer, it also decreases the amount of vitamin D that a person can make from sunlight.

To reduce the risk of skin cancer from sun exposure, the American Academy of Pediatrics recommends keeping infants younger than 6 months out of direct sunlight and protecting them with clothing and hats.

Other factors that decrease the amount of vitamin D a person can make from sunlight include:

• Living at high latitudes (closer to the polar regions), particularly during winter months.
• High levels of air pollution.
• Dense cloud covering.
• The degree to which clothing covers the skin.
• Use of sunscreen.
• Darker skin types.

Vitamin K is needed to form blood clots and to stop bleeding. Babies are born with very small amounts of vitamin K stored in their bodies, which can lead to serious bleeding problems like vitamin K deficiency bleeding (VKDB). VKDB can lead to brain damage and death.

Do infants get enough Vitamin K from breast milk?

No. Breast milk is low in vitamin K. Breast milk from mothers who are taking vitamin K supplements is also low in vitamin K.

The American Academy of Pediatrics recommends that all newborns, whether breastfed or formula fed, receive a one-time intramuscular shot of vitamin K1 (phytonadione) at a dose of 0.5 to 1.0 milligrams shortly after birth (this is usually given during the birth hospitalization).

A vitamin K shot can be administered after the first feeding at the breast, but not later than 6 hours of age. An oral dose of vitamin K is not recommended. Oral vitamin K is not consistently absorbed through the stomach and intestines, and it does not provide adequate amounts for the breastfed infant. Infants who receive the vitamin K shot do not require further supplementation.

A vitamin K shot given at birth is the best way to prevent low amounts of vitamin K and VKDB in infants.

Many new mothers wonder if they need to consume more calories (also called energy) during breastfeeding, but the answer is no. You can take in the same number of calories that you did before becoming pregnant. This strategy helps with weight loss after birth.

The Dietary Guidelines for Americans (DGAs) for caloric intake for all women 19 to 50 years old are based on activity level, as follows:

• Sedentary: 1,800 to 2,000 calories per day
• Moderately active: 2,000 to 2,200 calories per day
• Active: 2,200 to 2,400 calories per day

The increased caloric need for women who are breastfeeding is about 450 to 500 calories per day. Women who are not trying to lose weight following pregnancy should supplement the above DGA calories per day by 450 to 500 calories. Often an increase in a normally balanced and varied diet is enough to meet your body's needs. Whether or not to increase caloric intake during breastfeeding is a decision that should be made with the assistance of a health care provider.

Poorly nourished mothers, those on vegan diets or other special diets, and those with certain health conditions may require a supplement of docosahexaenoic acid (DHA) in addition to multivitamins to ensure complete nutrition for breastfeeding.

Women who are breastfeeding may have additional requirements for vitamins and minerals.

The estimated energy requirements (in calories per day) for infants are based on their age, size, and sex. Estimated energy requirements developed by the USDA are as follows:

Males

• 1 to 3 months: 472 to 572 calories per day
• 4 to 6 months: 548 to 645 calories per day
• 7 to 9 months: 668 to 746 calories per day
• 10 to 12 months: 793 to 844 calories per day

Females

• 1 to 3 months: 438 to 521 calories per day
• 4 to 6 months: 508 to 593 calories per day
• 7 to 9 months: 608 to 678 calories per day
• 10 to 12 months: 717 to 768 calories per day

The above daily calorie ranges are for infants of a specific weight and length.

The DGAs for infants increase as the infants get older. By the time that children are 2 to 3 years of age, daily calorie needs are 1,000 to 1,400 calories per day, depending on the child's activity level.

What is vitamin D supplementation for infants?

Although breastfeeding is the recommended method for feeding infants and breast milk provides most of the nutrients an infant needs, it does not provide infants with adequate vitamin D. Vitamin D is required to prevent rickets, a type of vitamin D deficiency. This disease is rare among breastfed infants but can occur if vitamin supplementation or exposure to sunlight is inadequate. (Exposure to sunlight helps the body to make vitamin D in place of supplementation.)

The current American Academy of Pediatrics (AAP)–recommended daily vitamin D intake is 400 IU per day for all infants and children beginning from the first few days after birth. Human breast milk contains a vitamin D concentration of 25 IU per liter (about 4 cups) or less. Therefore, to meet the 400 IU daily requirement, supplementation is required.

If an infant is weaned to a vitamin D-fortified infant formula and consumes at least 4 cups per day, then additional supplementation with vitamin D is not necessary.

When to Supplement Breastfeeding

Breastfeeding is supplemented by feeding an infant expressed breast milk from a bottle, formula, or breast milk from another mother. Such supplementation may be needed in the following situations:

In the Mother:

• Breast surgery or other trauma
• Primary breast insufficiency that prevents adequate milk production
• Physical separation from the infant
• Serious illness

In the Infant:

• Weight gain insufficient to maintain health (also sometimes called failure to thrive)
• Cleft lip and/or palate or other abnormality that prevents normal suckling ability
• Jaundice or liver problems
• Serious illness or prematurity that requires the infant to be cared for in a special nursery

Many of these conditions require a health care provider's care. You should always talk with your child's health care provider about whether to supplement your breastfeeding.

To keep supplementation from shortening or otherwise interfering with breastfeeding, you should supplement only after your infant is breastfeeding effectively and thriving on your breast milk.

Mixing Formula with Breast Milk

Mixing formula with breast milk in the same container is one way of supplementing breast milk. You may want to supplement your breast milk with infant formula if your milk supply is low or when you are physically separated from your infant.

Supplementing your breast milk with formula, however, may not be nutritionally the same as giving breast milk. Discuss the practice with your infant's health care provider before starting to mix formula with your breast milk.

Complementary Feeding

The term "complementary feeding" refers to giving your baby solid and liquid foods other than breast milk or infant formula. As babies grow, they have nutritional needs that breast milk or infant formula alone cannot meet. Complementary feeding helps meet those nutritional needs. It is also important for infants' jaw and muscle development and helps them develop speech later.

The AAP and the World Health Organization (WHO) recommend introducing safe, nutritious complementary foods into your infant's diet around 6 months of age. The exact timing depends on the infant's developmental readiness, meaning whether the baby can open his or her mouth and lean forward when interested in food. Studies show that introducing complementary foods before 4 months offers little health benefit to the infant and can increase the risk of food allergies and choking.

Some complementary foods are often called "baby foods" and can be pureed or mashed-up versions of meats, fruits, and vegetables. Different foods offer different nutrients. For example, around 4 to 6 months of age, babies' iron and zinc needs are higher than what breast milk or infant formula alone can provide. Complementary feeding of fortified cereals or pureed meats can provide these nutrients.

If you have any questions about complementary feeding, or if your family has a history of food allergies, talk to your infant's health care provider.