Last week I talked about high levels of manganese in drinking water being associated with reduced IQ. A related issue is baby formula – there is typically manganese in baby formula, and when mixed with water this could result in higher exposure than from water alone.
While my 3-month old is breast fed, we keep some formula around for emergencies, so I looked at a can we had sitting in the cupboard. Once diluted, the manganese concentration is reported to be 0.0050 mg per 100 mL (or 0.05 mg/L to put it into more standard units). Since last week I concluded that the Health Canada guideline of 0.15 mg/L was probably ok based on the data we have now, that doesn’t seem to bad.
However, there are two other factors that have to be considered. The first is that the actual exposure for an infant may be different than a child, due to different ingestion rates per body mass. The second is that there is already manganese in the water.
First, the dose. The study I looked at last week was based on children, so I’ll start by converting a concentration of 0.15 mg/L to a dose for a child. I’ll use typical characteristics recommended by Health Canada for a child between 5 and 11 – a body mass of 32.9 kg and water ingestion rate of 0.8 L/day. This results in a dose of 0.00365 mg per kg body weight per day (mg/kg/d). For an infant, Health Canada suggests a body mass of 8.2 kg and a water ingestion rate of 0.3 L/d. The 0.05 mg/L in formula then works out to 0.00182 mg/kg/d. Still about half of our assumed safe dose.
However, we still have to add in manganese from the water used to make the formula. The assumed safe dose of 0.00365 mg/kg/d is equivalent to a concentration in formula of approximately 0.1 mg/L. We already have 0.05 mg/L from the formula mix, so that only allows another 0.05 mg/L from water. Suddenly we’re dealing with concentrations that are well below the current drinking water guideline. Health Canada found concentrations higher than this in 25% of drinking water supplies tested – which means a significant number of formula-fed infants could be exposed to manganese doses greater than this assumed safe dose.
There are certainly a lot of assumptions made here – including that the manganese effects are the same in infants as in children and at similar doses (infants could be either more or less sensitive), and that the manganese in formula powder is equally available to the digestive system and in the same chemical form as manganese in tap water. There’s also still a lot of uncertainty in just what exact dose or concentration of manganese causes IQ effects.
While manganese is an essential nutrient, deficiency is rare, and concentrations in formula are much higher than concentrations in breast milk (which are typically around 0.005 mg/L). Therefore, it seems it would be prudent to try to reduce manganese concentrations in formula to the lowest levels possible.