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I realize that this question can have many personal or subjective viewpoints, so the answer I'm looking for is what the best-known data shows us from two perspectives:

  1. Is there an average breastfeeding duration that is found in other mammals? This should perhaps be normalized based on the gestational period.

  2. What does the data say about breast milk providing continued benefit? In particular, is there a certain age or weight after which breast milk no longer provides measurable or worthwhile benefit?

Essentially, a good answer will be backed by science and research, not personal opinion.

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    I don't think you should consider weaning time in other mammals when deciding how long (or short) to breastfeed your child. In the wild, mothers are incentivized to shorten weaning times since breastfeeding incurs a cost of a significant number of calories on the mother. In fact, in situations where food is scarce, a mother will stop nursing even if that means her baby will starve to death. The weaning time in nature has evolved to be a balance between what is best for the baby and mother, whereas I suppose you want what's best for the baby, since you (presumably) aren't facing starvation.
    – Scott Mitchell
    Commented Apr 13, 2011 at 4:48
  • @Scott - Good point, but I think if you find a statistical average and look across different mammals in different environments and geographies those anomalies will work themselves out. What might be interesting is looking at samples from zoo animals that don't face predators or food shortages.
    – J.J.
    Commented Apr 13, 2011 at 4:54
  • @Javid: I am doubtful that averaging it out across all mammals would erase the conditions I speak of. I presume the average weaning time is instinctual. Yes, it is shortened if there are calamitous conditions, but I doubt it is lengthened in the good times. Evolutionarily speaking, a child has every incentive to nurse for as long as possible, while a mother has every incentive to keep that time as short as possible while still ensuring her child lives long enough to reproduce. As humans, we can overcome evolutionary pressures via rational thought, but not so for lower-order mammals.
    – Scott Mitchell
    Commented Apr 13, 2011 at 5:00
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    @Scott - I think your concern / assumption is that the average time for other mammals will be shorter than humans (based on modern 1st world country statistics). I going to wager that the data will show the opposite. I think that most mammals will probably breastfeed for 2.5 - 3 times the gestational period, which would be about 22 - 27 months for humans. I would wager that actual modern averages for humans are no more than 15 months, if that. But, I'm note sure, hence the question. Either way, knowing the statistics for other mammals will be an interesting data point.
    – J.J.
    Commented Apr 13, 2011 at 5:15
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    @Javid Jamae: Our closest relatives, Chimpanzees-Gestation 232 days, weaning 4-5 years. White tailed deer--Gestation 28 weeks, weaning 5 weeks. Lions are in your hypothesized space (110 days/120-150 days) but there isn't any particular reason to consider Chimps, Deer, Harbor Seals, and Grizzlies as outliers and Elephants, Wolves, and Lions as normative. I think that if you plot a few dozen mammal species, you'll see a continuum from Harbor Seals to Chimpanzees. If you want to know the optimum nursing time for human children, you'll need to look at the literature for humans.
    – philosodad
    Commented Apr 15, 2011 at 21:23

5 Answers 5

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TL;DR - exclusive breastfeeding: 6 months, partial breast-feeding: 12 months or longer

Well, since you asked about research papers, here they are.

The optimal duration of exclusive breastfeeding: a systematic review. (abstract) (2004)

Based on the results of this review, the World Health Assembly adopted a resolution to recommend exclusive breastfeeding for 6 months to its member countries.

I did not find a study that explicitly aims to establish when to stop breast feeding completely. However there is a number of articles that research connection between length of breast feeding and various development and health parameters.

All of the ones I found relevant clearly show that it is beneficial to partly breast-feed a child at least up to 12 months. Sources, links and summaries are below.

Breast feeding and cognitive development at age 1 and 5 years [PDF] (2001):

Children breast fed for less than 3 months had an increased risk, compared to children breast fed for at least 6 months, of a test score below the median value of MDI at 13 months and of WPPSI-R (Wechsler Preschool and Primary Scales of Intelligence) at 5 years.

Duration of Breastfeeding and Risk of Overweight: A Meta-Analysis (Sep. 2005)

the duration of breastfeeding was inversely associated with the risk of overweight (regression coefficient = 0.94, 95% confidence interval (CI): 0.89, 0.98). Categorical analysis confirmed this dose-response association (<1 month of breastfeeding: odds ratio (OR) = 1.0, 95% CI: 0.65, 1.55; 1–3 months: OR = 0.81, 95% CI: 0.74, 0.88; 4–6 months: OR = 0.76, 95% CI: 0.67, 0.86; 7–9 months: OR = 0.67, 95% CI: 0.55, 0.82; >9 months: OR = 0.68, 95% CI: 0.50, 0.91). One month of breastfeeding was associated with a 4% decrease in risk (OR = 0.96/month of breastfeeding, 95% CI: 0.94, 0.98).

Breast feeding and obesity: cross sectional study (1999)

A clear dose-response effect was identified for the duration of breast feeding on the prevalence of obesity: the prevalence was 3.8% for 2 months of exclusive breast feeding, 2.3% for 3-5 months, 1.7% for 6-12 months, and 0.8% for more than 12 months.

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The American Academy of Pediatrics recommends exclusive breastfeeding for the first 6 months, followed by continued breastfeeding with complementary foods for a year, while the World Health Organization recommends exclusive breastfeeding for the first 6 months, followed by continued breastfeeding with complementary foods up to two years of age and beyond.

http://www.cdc.gov/breastfeeding/faq/index.htm

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I am really surprised no one mentioned Kathryn Dettwyler who has researched exactly the idea of what is normal for weaning in mammals & compared that to humans. She uses data such as age of mature teeth, puberty, etc to determine how the nursing length of species compared to one another & comes to the conclusion that natural human weaning would be somewhere are 2.5-7years. https://www.health-e-learning.com/articles/A_Natural_Age_of_Weaning.pdf

As far as after a certain age where it would be of no benefit, I can't find anything. Realistically I think it's likely more healthy for me to be putting human milk on my cereal than cow's milk but I am not likely to take up that habit. Human milk is better suited for human nutritional needs and it's composition is infinitely more easily digested than milk of other species. It would be reasonable then to presume that any potential benefits of dairy products would be of more benefit when made from milk of our species. This thinking is so accepted by some that there is a market among body builders & athletes now to purchase breast milk. I personally stick to good multivitamins & work on a solid diet, as I personally have no interest in consuming it. I have gargled it though & it works wonderfully on a sore throat.

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Infants are given a natural immune boost at birth, 6 months when they begin exploring their world and then again at 12 months. It is recommended that a child breast feed exclusively for the first 6 months, but some start more solid food as early as 4 months. My goal was to breast feed for one year and my first child weaned himself within days of his first birthday. I have heard many parents use the argument of continuing to nurse through the toddler years (age1-3) to help with the child's frustration. I have seen that work for some children, and I have also seen it hinder some childrens development of other coping strategies. Some children that are breastfed longer tend to not get sick as often, or when they do it sees to be less severe. In terms of physical benefit-one year seems to be the final time where they get what they NEED. The best method of determining when a child no longer needs to be breastfed is by following the child's natural lead and finding out what works for the family, child included.

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  • Thanks for the answer, but the question is not around the psychological needs of breastfeed (for the mother or child), or whether children can get nutrients or immune boosters in non-natural ways. The questions is whether breastfeed, in and of itself, has continued biological benefits, or lack thereof.
    – J.J.
    Commented Apr 14, 2011 at 17:04
  • why are you not considering psychological benefits? Surely you are interested in the complete development of the child? This is one of the reasons its difficult to compare to other mammals - since we know less about their psychology
    – SarahM
    Commented Jul 5, 2011 at 21:53
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You cannot compare other mammals to humans. Each mammal species has their own diet, which directly influences the nutrients in the mother's milk.

Because humans have such a diverse diet within our species (some of us being vegans, vegetarians, etc), you cannot compare the human species (as a whole) to other mammals.

If the mother follows a healthy diet, she can breastfeed the baby for up to four months exclusively. To gauge if the baby is getting enough nutrients, you'll have to keep stats on the number of dirty diapers. If the number goes down, the baby is not getting enough nutrients and it might be time to introduce solid foods.

http://www.womenshealth.gov/breastfeeding/

How long the mother breastfeeds for depends on the benefits the child gain from it, which in turn depends on the health of the mother and child. For example, breastfeeding can greatly reduce the risk of obesity in children 39 to 42 months (from ‘trusty’ ol’ Wikipedia http://en.wikipedia.org/wiki/Breastfeeding). It also reduces the risk of coronary heart disease by as much as 23% if the baby is breastfed for at least 24 months.

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    -1: doesn't answer the question. I didn't ask how long you "can" breastfeed. Sure most women can breastfeed for 4 months. Then again, most can do it for 5, 6, 7, or 8, or 20 months. The question was asked to gain an understanding of whether there was a point of diminishing returns. And to say that you "can't" compare to other mammals is entirely wrong. Sure you can. Its a valid data point, and perhaps very meaningful. Are you stating this as an expert in the area, or is this just your personal opinion?
    – J.J.
    Commented Apr 13, 2011 at 13:19
  • No I'm not an expert, (for that you should consult a paediatric forum). If you truly want an objective answer you have to narrow it down to a group of humans who follow a balanced diet. Surely you can’t use a lactating mother with excellent health and a starving mother in the same comparison to mammals. Rather rephrase your question to “Evolutionary and energetic elements of human lactation compared to other mammals”
    – Celeste
    Commented Apr 13, 2011 at 13:43
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    @Javid Jamae: Wolf cubs are born blind and essentially helpless, but Elephant calves can walk almost immediately. Human children are born completely helpless and they develop more slowly than many other mammals. Lifespans, social structures, diet, environment, and developmental rates are totally different for different species, and all of these things affect the nursing period. Maybe I'm missing something, but, I just don't see how it is meaningful to compare the duration of nursing between Humans and Harbor Seals.
    – philosodad
    Commented Apr 15, 2011 at 3:51

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