Elevated estrogen metabolites in the body are seen to be associated with certain cancers, including prostate, ovarian, and breast cancers. One potential dietary source of these metabolites that is commonly consumed is milk. Let’s look at how cow and goat milk vary in their estrogen levels.
What does the research say about dairy and cancer?
Many studies have looked at dairy intake and cancer risk, but the results aren’t clear. Some studies show strong links; others don’t show any association. There are many mechanisms through which dairy might affect cancer risk. These include calcium, vitamin D, estrogen hormones, and insulin-like growth factor. The different study outcomes may be due to some of these factors counteracting each other. However, as estrogens are considered a major pathway to certain cancers, the influence of dairy intake on estrogen should be strongly considered.
The most popular milk – cow or goat?
In Northern America and many developed countries, the primary source of dairy is from cows. Surprisingly, goat milk is the most ingested milk globally. Given the concerns over regular milk consumption and increased cancer risk, it is useful to compare goat and cow milk and countries where it is consumed to see if one seems preferable to the other.
Goats as a dairy source have risen in popularity in recent years as they require much less land than cows. The growing ethnic diversity in the US is also considered to have affected its popularity. The top producers of commercially available goat milk have increased production more than 30%. However, the goat milk industry in the US has not flourished, and it is mainly sold only in specialty stores or directly from farmers. Most milk in the US still comes from cows.
Research on milk Estrogen levels
As milk and dairy are frequently consumed on a daily basis throughout life, it is estimated that their consumption accounts for 60-70% of the total estrogen consumption. This warrants continued research into the risk this poses for cancer and other diseases.
Farlow et al., (2012) conducted research on estrogen content of commercially available milk. The bar chart below comes from the research: Journal of Dairy Science, Vol. 95, No. 4, 2012, page 1707. It shows total estrogen content in 7 selected milk samples – 6 from cows and one from goats.
The results indicate that estrogens were significantly lower in goat milk compared with the cow milk tested.
It may seem surprising that total estrogens in organic milk were higher than regular cow milk. While organic milk may not have an advantage of lower estrogen levels over regular milk, it does have fewer pesticides and growth hormones.
Using these results and relaying them back to daily consumption of dairy, the researchers found that the average level of intake of estrogen per day is:
- 24-54 ng (nanograms) per day for cow milk drinkers (based on 3/4 cup milk/day)
- 10 ng per day for goat milk drinkers (based on 3/4 cup milk/day)
While it may be only a small amount a day, the cumulative effects of years of consumption are still unknown.
From these results, the authors conclude that for individuals concerned with steroid hormone consumption, consuming goat milk and dairy would be a preferable choice over cow dairy. While we should all be concerned about steroid hormone consumption, this is particularly important for those at high risk of hormonal cancers or who have been diagnosed with these cancers, e.g., prostate, breast and ovarian.
Why the big difference between goats and cows?
One of the reasons for the difference between cows and goats milk estrogen content is because a lot of our cow milk comes from pregnant cows. When pregnant, the animals have elevated estrogen levels – up to 33 times higher estrogen than non-pregnant levels. Grass-fed organic dairies also milk pregnant cows. This explains why organic cow milk doesn’t have lower total estrogen levels than non-organic cow milk. Generally, cows produce a calf a year. They have the same gestation period as humans – 9 months – and get two months off from milking during that time. This means that for seven months of each year for each cow, we get “pregnant” (i.e., high estrogen level) milk.
With goats, they have only a five month gestation period. It is standard practice is to stop milking three months into a pregnancy, and then give them two months after birth to feed their young. This means that if goats breed once a year, we only get “pregnant” milk for three months out of the year.
Take home message
Eating goat dairy results in a much lower intake of estrogens in our diet than consuming cow dairy. Yes, compared to hormone replacement and contraception, the estrogen levels of both cow and goat milk are relatively low. However, let’s not ignore milk’s often daily estrogen contribution, throughout most people’s lives.
And while goat may seem preferable over cow milk for estrogen intake, there are now all the non-dairy kinds of milk out there today too, and nut milk doesn’t contain any estrogens.
If you drink cow milk/cheese, try a goat or nut milk/cheese this week instead. There is so much choice out there.