- Background on Hypospadias
- Research on Vegetarians
- Possible Connections
Background on Hypospadias
Hypospadias is a male birth defect in which the opening of the urethra—the tube through which urine passes—isn’t located at the tip of the penis as it should be. It’s believed to be caused by a combination of genetic susceptibility and environmental factors including environmental contaminants (1, 2).
As of 2012, the nationwide rate of hypospadias for the USA was about 64.7 cases per 10,000 male live births, or 1 in 155 male live births (3). Some forms of hypospadias are relatively easy to repair with surgery done on an outpatient basis and surgical repair usually results in a penis with normal, or near-normal, function and appearance (4).
Research on Vegetarians
As of May 2018, there have been six studies comparing hypospadias cases in boys born to vegetarians versus non-vegetarians. Table 1 lists them.
|Table 1. Rate of hypospadias cases in boys born to vegetarian mothers|
|Study||Type||No. of Boys||Cases||Vegetarians||Vegetarian cases||Rate|
|UK 2000 (5)||Prospective||6296||51||321||7||3.53 (1.56, 7.98)|
|Netherlands 2007 (6)||Case-Control||834||583||17||10||0.6 (0.3, 1.6)|
|Sweden & Denmark 2008 (7)||Case-Control||719||291||22||14||4.6 (1.6, 13)|
|UK 2009 (8)||Case-Control||949||467||168||77||0.85 (0.61, 1.2)|
|India 2011 (9)||Case-Control||200||80||123||52||1.28 (0.71, 2.3)|
|USA 2012 (10)||Case-Control||4368||1250||43||10||0.6 (0.3, 1.2)|
The first study to examine the link (UK, 2000), found that a vegetarian diet in pregnancy was associated with a 3.5-times higher risk of having a son with hypospadias compared to a non-vegetarian diet in pregnancy (5).
Two of these studies deserve more weight—the 2000 UK study which found a link between vegetarian diet and hypospadias, and a 2012 USA study which did not.
The 2000 UK study is a prospective study and prospective studies generally hold more weight than do case-control studies because they involve less risk of mischaracterizing dietary patterns. However, in the case of vegetarians and hypospadias, mischaracterizing dietary patterns in case-control studies is probably not much of an issue because diet recall happened shortly after hypospadias diagnosis.
The 2012 USA study was very large, making random chance findings unlikely. In fact, it contained almost 25 times as many cases of hypospadias than did the 2000 UK study. Additionally, these two studies were designed with the purpose of investigating vegetarian diets while the aims of the other studies were broader.
Thus, the two most important studies have differing findings, though reason to put significant weight on the 2012 USA study.
It’s important to be aware that the cause of most cases of hypospadias is unknown. There appear to be many genetic and environmental factors (11) so pinpointing a single cause may not be possible. The different results in studies of vegetarian diets and hypospadias risk could be chance or could be due to differences in food choices, supplement use, environmental exposure, or something else.
With that in mind, what are some possible explanations for the higher risk seen in vegetarians in two studies?
A first guess would be that vitamin B12 deficiency among vegans and even some lacto-ovo vegetarians could have increased the risk of hypospadias. At least one study has found a link between vitamin B12 deficiency and hypospadias (11).
The UK study examined births between 1991 and 1992 (5). The USA study examined births between 1997 and 2005 (10). And in the years between when these two studies were conducted, there was much education in the vegan community about the need for vitamin B12, which could explain why the risk might have disappeared.
However, there are many documented cases of vegan infants whose mothers had been deficient in vitamin B12 and to none of these boys have been reported to have been born with hypospadias (more info).
Whether or not a lack of vitamin B12 increases the risk of hypospadias, it plays other important roles so all pregnant women should have a reliable daily source of vitamin B12—see Daily Needs.
Folic Acid and Methionine
What about other molecules involved in one-carbon metabolism such as folate (or folic acid), choline, and methionine?
There’s a bit of evidence that methionine could play a role (13).
In a report coming from the National Birth Defects Prevention Study (USA, 2009), women taking supplemental folic acid and who ate more than 1,870 mg/day of methionine had a 40% reduced risk of having a baby with hypospadias (0.6, 0.4-0.9). Since no effect of methionine was seen in women who did not take folic acid supplements, it’s possible that the results are mainly due to the folic acid supplements.
Still, methionine is an essential amino acid. The RDA is well under 1,870 mg/day for most pregnant women. Without more evidence, it’s probably unnecessary to strive for 1,870 mg per day. However, it’s a good idea to make sure a pregnant vegan’s diet has plenty of methionine.
The plant foods highest in methionine are tempeh, peanuts, oatmeal, quinoa, and spaghetti—see Protein and Amino Acid Content of Selected Plant Foods.
Choline, a nutrient that can be on the low end in vegan diets, was investigated in the National Birth Defects Prevention Study (13). They didn’t find a statistically significant association between high choline intake and risk of hypospadias (0.7, 0.5-1.1), but it’s still a nutrient for pregnant vegans to be aware of—see Choline.
Parental exposure to pesticides through work or residential lawn care is associated with increased risk of hypospadias in some, but not all studies (1, 16). Dietary exposure to pesticides has been estimated in some studies by examining the use or purchase of organic vegetables. For example,2000 UK study also examined the purchase of organic vegetables.
The authors state:
Unfortunately, only 163 mothers always bought organic vegetables; that none of these mothers had a son with hypospadias is of some interest, but only one case would have been expected. No reduction in risk was evident among those who ‘sometimes’ bought organic vegetables (0.8% had hypospadias, compared with 0.6% who never bought organically grown vegetables) (5).
A study from Denmark found no association between use of organic vegetables and fruits and risk of hypospadias (16).
While there might be something to the pesticide/organic vegetable link, there doesn’t seem to be enough statistical power to draw any conclusions.
Finally, there is soy, a food no discussion on vegetarianism should ever be without! The concern is that the plant estrogens in soy might interfere with the sexual development of boys.
While there was a trend in the 2000 UK prospective study for a higher risk of hypospadias with drinking soy milk versus not (3.7, 0.87-15.4), and for eating soy meats more than once a week versus never (2.95, 0.90, 9.68), the findings were not statistically significant (5).
Eating beans (not soybeans) was associated with an even higher risk of hypospadias which makes it less likely that plant estrogens are the cause of the increased risk of hypospadias since beans (other than soybeans) contain only very small amounts of plant estrogens. In this study, it might have been hard to separate eating soy milk and meats from simply being vegetarian.
A 2012 study from the USA (18) found reduced risk of hypospadias with higher intakes of some plant estrogens. A 2004 study from the Netherlands (17) measured soy intake and hypospadias and found no link for maternal soy intake. Results are in Table 2.
|Table 2. Hypospadias & Soy (2004)4|
|Soy Protein Intake|
|0 to 20 g/day||1.1 (.5, 2.5)|
|20+ g/day||1.0 (.5, 2.2)|
Under the worst-case scenario, based on the 2000 UK study, a vegetarian mother would have a 4% chance of having a baby with hypospadias. The trend since that first report has been to find no association between a vegetarian diet and hypospadias and that is punctuated by the most recent 2012 USA study with almost 25 times as many cases of hypospadias than the 2000 UK study. This gives reasonable confidence that a vegetarian diet is not a significant risk.
Making sure pregnant vegans get enough folic acid, vitamin B12, methionine, and choline can help alleviate any potential risks.
Last updated May 2018
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