Baby formula

Breastfeeding vs Formula

Every public health organization will encourage exclusive breastfeeding for at least the first 6 months of life. There is good reason for that: For one breast milk is the most nutritionally complete food a newborn can eat. In addition, breast milk allows antibodies from the mother to pass to the infant via the milk, effectively short-term boosting their immune system.

This gave us the omnipresent “Breast is best” slogan. I’m neither qualified nor I have the intention to disagree; However, it is quite common for “breast is best” to transform into “breast is the only option”. In this section I will argue that “Breast is best, but formula is also OK”.

Some important background: Starting around 1920 formula manufacturers began aggressively marketing it as a better alternative to breast milk. These marketing tactics are now widely considered as predatory, reaching levels where physicians were being paid to convince new parents to switch to formula feeding alleging false health benefits.
This led to a steady decrease in breastfeeding rates across the world, creating suboptimal health outcomes. This was especially pronounced in the underdeveloped regions where access to clean water and sanitary conditions of preparation is limited.

As a response WorldHealthOrganization and Unicef created the Baby-Friendly Hospital Initiative, which instructs health professionals on providing guidance and promoting breastfeeding. You can read more about this from WorldHealthAssociation directly or from here. Overall a positive change, but it had the unfortunate outcome where in some cases “encouragement” becomes societal pressure (E Grattan et al).

In addition to the above, there is another complicating factor:
All research on breastfeeding is observational. Instead of a designed study with randomized groups, participants self-select into breastfeeding vs non-breastfeeding groups (for obvious ethical reasons researcher’s can’t discourage breastfeeding to “see what happens”). Families with high socio-economic status are more likely to breastfeed (Martje Van Neste et. al.) but the same cohort of people have access to better medical care, not smoke, be better informed on safe sleep practices and in general have more positive health outcomes. With all these confounding factors attributing a particular benefit to breastfeeding becomes tenuous. The PROBIT and the Improved Estimates of the Benefits of Breastfeeding Using Sibling Comparisons to Reduce Selection Bias studies try to address this bias and concluded that

nonexperimental studies of breastfeeding overstate some of its other long-term benefits, even if controls are included for race, ethnicity, income, and education.

Hank Green explains much more eloquently this point in this 13 minute SciShow video.

The point I’m trying to make here: Even trustworthy sources will occasionally oversell the benefits of breastfeeding while casting formula in an exaggerated negative light. Sometimes even the scientific community over-corrects and swings in the opposite end of the spectrum.

If a mother desires and is able to breastfeed exclusive breastfeeding until 6 months is indeed the ideal option. If not formula feeding or supplementing is also a perfectly viable option. Baby formula is one of the most tightly regulated food items on the market and is the only existing alternative to breast-milk suitable for newborns. In 2026 only 52% of newborns were exclusively breastfed for the first 6 months.

[!WARNING] All of the above applies to a healthy baby that was delivered on term. Babies born preterm or with very low weight are at higher risk for Necrotizing Enterocolitis. Human milk has a demonstrated protective effect against this disease.

Bacteria and the role of hygiene in formula preparation

This section contextualizes why preparation guidelines were created and what they are designed to protect against. With context established the reasoning behind every “step” should become self-evident.

Guidelines for the preparation and storage of powdered infant formula focus primarily on preventing contamination and limiting bacterial growth. The two main risks are Cronobacter sakazakii (Enterobacter) and Salmonella enterica contamination. PMC6874386. These bacteria occur naturally in the environment and pose little threat to a healthy adult but can be dangerous to a newborns. While all infants are vulnerable, those under two months face a heightened risk, and babies born prematurely or with weakened immune systems are in the highest risk category.

Both above-mentioned bacteria can survive in dormant form even in dry environments but start rapidly multiplying when water is introduced.

While contracting a disease from these bacteria is unlikely, proper handling is essential since these infections can be extremely serious if they do occur. According to sections 1.2.1 and 1.2.2 of the WHO report on safe formula handling and PMC6874386

In the United States of America, an incidence rate of 1 per 100 000 infants for E. sakazakii infection has been reported. (2006)

The United States of America reported a salmonellosis incidence rate of 139.4 cases per 100 000 infants in 2002.

(E. sakazakii ) It has an incidence of 2–5% in premature infants and 13% in those weighing less than 1.5 kg at birth.

Powdered infant formula can get contaminated in three ways:

• During production: Formula manufacturing is strictly regulated and plants are often inspected but PIF is not a sterile product. Although rare, contamination sometimes occur during production. When this contamination is detected the affected batch is recalled.
• From water used for mixing.
• From the environment during preparation. (dirty surfaces, unsanitized hands etc.)

By following proper preparation procedure both the risk of contamination is greatly reduced, but also ensures any potential bacteria already present in the powder is not allowed to multiply, so it can be handled by the newborn’s immune system.

Tap or bottled Watter

Using boiled tap water is the most common way to prepare baby formula, assuming your tap water is safe for human consumption.

Some countries add fluoride to their drinking water supply for its beneficial effect on dental health. Fluoridated tap water is considered safe for formula preparation and health authorities don’t currently advise parents against using it. If water fluoridation is one of your concerns see Annex: Fluoride in tap water for a deeper dive.

Bottled water is not recommended for formula preparation. Just like tap water it is not sterile and needs to be boiled before mixing. Additionally, bottled water can contain a high level of sodium (which can cause salt toxicity in newborns PMC4500422) and other minerals that can put strain on infant’s kidneys.

If you must use bottled water, avoid natural mineral water and opt for low mineralization water instead:
Ideally the bottled water for formula preparation has a dry residue <250 mg/L and sodium <20mg/L (non-academical sources glenaqua.es and hydrasana.com)
These numbers are not set-in-stone but should give you a frame of reference. For scale: a popular high minerality natural water in my region has a dry residue of 3052 mg/L and a sodium content of 1097 mg/L, making it clearly unsuitable for infant consumption.

Boiling and water temperature when mixing

Guidelines from both the NHS and WHO instruct boiling the water and mixing the powder while the water is at no less than 70 degrees Celsius.

Boil the water. Then leave the water to cool for no more than 30 minutes, so that it remains at a temperature of at least 70C. NHS

Taking care to avoid scalds, pour the appropriate amount of boiled water, which has been allowed to cool slightly, but not below 70 °C. WHO

CDC on the other hand recommends using cold tap water for most cases CDC - formula preparation and storage but boiling and mixing at 70 degrees only for high-risk groups: less than 2 months old, born prematurely or ones with weakened immune systems. CDC - extra precautions

To make things even more confusing the preparation instructions on some cans of formula instruct the caretaker to boil the water but cool it to less than 40 degrees before adding the powder. For example instructions on Nestle’s NAN 1 Infant Formula

Why these guidelines differ and what’s the right way to do it?

Firstly by boiling the water any potential bacteria contained in water is eliminated, secondly by adding the powder in at 70 degrees or above any potential bacteria already present in the powder is destroyed. This way of preparing PIF is the safest and virtually removes all possibilities for getting sick from Cronobacter. See Bacteria and hygiene in PIF preparation and NEC for a more detailed explanation.

Why then the contradictory recommendation from CDC and formula manufacturers?

Some modern formulations of baby powder contain probiotics which are destroyed when the powder is mixed with hot water. If your chosen formula brand has added probiotics or other heat-sensitive ingredients it will likely instruct you to mix the powder with cold water.

Secondly, boiling water before every feed (once every 3 hours) is highly impractical in a household setting, often making caretakers prepare large batches at once and storing them improperly.

What I ended up doing myself:

I am against preparing formula in large batches. While it is safe to store formula at <5 Celsius for up to 24 hours, if my fridge fails to maintain the low temperature for any reason (power outage, door left open, fauly sensor, etc) any contaminants in the already mixed feed will multiply aggressively.

By using room temperature water and mixing one feed at a time before serving I can ensure that in the unlikely chance that bacteria is present in the powder, it does not get a chance to multiply and it can be handled by my daughter’s immune response. I used pre-boiled watter (that was stored in the same pot used for boiling, with the lid on)

Choosing formula brands

Work in progress.

Annex: Fluoride in tap water

Fluoride is a naturally occurring mineral that is often added to drinking water supply for its beneficial effect on dental health. In very high doses this mineral becomes toxic, and often in online forums concerns are raised around using fluoridated tap water for formula preparation. The reasoning behind this concern is that formula-fed newborns will consume much more fluoride per kg of body weight than a breastfed baby or an adult.

Water fluoridation was not a particular concern in our case and we used boiled tap water for preparing infant formula, but I feel this topic deserves representation and some scrutiny as it is very often miss-represented.

The impossibility of acute fluoride poisoning from fluoridated tap water:

In the US the maximum allowed fluoride concentration in tap water is 0.7mg/L while in europe the maximum permissible concentration is at 1.3mg/L. In high concentrations fluoride is indeed toxic, the lethal dose for an adult is 64mg/kg of body weight. Babies are not adults, but extrapolating it would mean that a 3kg baby would need to consume 274 liters of water in one sitting suffer deadly fluoride poisoning (3*64/0.7).

In concentrations of 0.3 mg/kg of body weight fluoride is not life-threatening but can cause gastrointestinal discomfort. That would mean that the same 3kg baby would need to consume more than one liter of water in one sitting to experience the side effect. Reference numbers from wikipedia and US National Institute of Health. Obviously these numbers are ridiculous, which is corroborated by the reference material.

This dose would be virtually impossible to achieve from water or toothpaste containing standard levels of added fluoride.

Historically, most cases of acute fluoride toxicity have followed accidental ingestion of sodium fluoride based insecticides or rodenticides.[10] Currently, in advanced countries, most cases of fluoride exposure are due to the ingestion of dental fluoride products

Effects of long term exposure to fluoride:

Things are less clear-cut when conversation shifts towards the side effects of long term exposure to smaller doses. The scientific consensus leans towards “artificially fluoridated water is safe for formula preparation” but there is some debate for this.

One of most common effects of prolonged intake of high levels of fluoride is dental and skeletal fluorosis.

Dental fluorosis

Dental fluorosis is a cosmetic condition that alters the appearance of the tooth enamel, changing its color to a more yellow tint. The effects are cosmetic only, does not affect tooth function and is not painful CDC article. To reduce the risk of dental fluorosis EFSA (European Food Safety Authority) recommends an intake of maximum 0.05mg fluoride per kg of body weight per day.

Balancing the benefits of caries prevention against the risk of dental fluorosis, EFSA recommended an AI of 0.05 mg fluoride/kg b.w. per day from all sources for children and adults, PMC7261729

The hypothetical 3kg baby used for calculations would need to consume around 2 liters of fluoridated water at 0.7mg/liter to be at risk of dental fluorosis. Developing dental fluorosis from drinking water alone is possible but very unlikely.

Skeletal fluorosis

Skeletal is a bone disease caused by deficient mineralization of the bones making them more prone to fractures. This is a more serious condition but is reversible in some cases if fluoride intake is stopped.

Skeletal fluorosis is endemic in several countries where the potable water sources naturally contain high fluoride levels (>4 mg/L), and where water consumption is high due to hot climates (EFSA 2013). Fluoride intakes of above 6–8 mg/day may increase the risk of bone fractures PMC7261729

At fluoridation levels of 0.7 mg/L to consume 6 mg of fluoride one must drink around 8.5 liters of water daily for a significant amount of time.

Association between IQ and fluoride consumption

Some studies point out an association between diminished non-verbal intellectual abilities and water fluoridation.

Exposure to increasing levels of fluoride in tap water was associated with diminished non-verbal intellectual abilities; the effect was more pronounced among formula-fed children. PMC6913880

Others claim no correlation and re-state the safety of water fluoridation.

This population-based follow-up study has provided consistent scientific evidence that early-life exposure to fluoride was not negatively associated with cognitive neurodevelopment. The findings, in combination with the current body of knowledge, provide assurance that the currently practiced WF programs are both effective and safe for young children. PMC11843800

These meta-analyses show that fluoride exposure relevant to community water fluoridation is not associated with lower IQ scores in children. S0033350623000938

This rapid systematic review indicates that community water fluoridation at concentrations between 0.7 and 1.0 mg/L is not associated with adverse nondental health effects in the general population. However, exposures exceeding the WHO guideline of 1.5 mg/L may increase risk of health effects, particularly among children and other susceptible groups. S2161831325001851

In conclusion: At current maximum allowed levels of fluoridation 0.7mg/L in US and 1.3mg/L in EU developing negative health outcomes from consuming fluoridated water is virtually impossible. Fluoridated water is considered safe for formula preparation and health authorities don’t currently advise parents against using it.

Annex: NEC and Preterm or Low birth weight infants

Necrotizing enterocolitis is life-threatening gastrointestinal disease affecting predominantly newborn babies. The exact cause for it is unknown. It manifests as an inflammation of the intestine which allows bacteria to infiltrate the colon tissue. More about it here.

This disease typically occurs in 2-6 weeks after birth. Babies born with low weight or under 28 weeks of gestation are especially vulnerable. It affects 2-5% of premature infants according to the study Jacob G. Ginglen, Nikolai Butki.

Formula feeding has been identified as one of the primary risk factors for developing NEC. Studies like A. Lucas and T.J Cole suggest a 6-10 times decrease in incidence for breastfed babies, and 3 times less common in babies who were mixed fed. (I can’t find the original paper, sorry).

For high risk babies, breastfeeding is highly encouraged for this reason. In case breastfeeding is not feasible, some NICU units offer access to pasteurized donor milk.

If formula feeding is the only option, WHO recommends using Sterile ready-to-feed (RTF) infant formula when possible. It is pasteurized during production and has the lowest risk of being contaminated during handling by the caretaker.

Where feasible, sterile liquid infant formula should be used in care settings, especially when feeding highrisk infants. These feeds do not contain harmful bacteria. Care settings, such as neonatal intensive care units, provide care for infants at greatest risk of E. sakazakii infection, i.e. neonates and those less than two months of age. However, sterile liquid infant formula is not always available (e.g. for infants who have special dietary needs), and PIF might be used instead.

Section 2.2.1 of Safe preparation, storage and handling of powdered infant formula Guidelines

If you are in this situation, definitely have discussion with your healthcare professional and do not rely on general guidelines.