In 1935, a Swedish professor named Erik Agduhr published a paper in Zeitschrift für Vitaminforschung entitled “Ergosterol increases the prolific capacity of the experimental animals, and normal sexual functions intensify their resisting power against the toxicity of the ergosterol.” In the paper, he describes experiments wherein he gave just under a hundred mice either 4,000 or 8,000 IU per day of irradiated ergosterol, known more simply as vitamin D2. These are huge doses for such little critters. But, you know how they do: give mice enough vitamin D and you'd swear they were bunnies.
Mice getting both doses of vitamin D were kept in a cage with one or a few other mice of the same sex. Some of those getting the higher dose, and some eating a control diet, were kept in mixed-sex cages and allowed their conjugal rights. If the females got pregnant and gave birth, their pups were immediately killed “in order to release the female from the exertion of the organism a lactation might give rise to,” a process known in the past as infanticide (at least when humans do it to their own children), but recently advocated in the BMJ Group's Journal of Medical Ethics as “after-birth abortion.”
Over the course of 40 weeks, lady mice in the control group found buns in their ovens on average only 5.2 times (yes, even normal mice are prolific), whereas lady mice getting the toxic level of vitamin D and caged up with hubbies getting the same found themselves in such straits 8.7 times. From these numbers, vitamin D would appear to be the original Viagra (or Clomid?): toxic doses of it increase “the prolific capacity” of mice by 67%.
But there's more! All this party time the mixed-cage male mice were getting really seemed to save their lives. Males caged only with other males were dying left and right while they were consuming toxic doses of vitamin D. Just under half of the dude mice getting the low dose died, while just under 65 percent of those getting the high dose died. Only seven percent of dude mice getting the high dose of D but caged with the fairer sex left this world for the next!
Female mice were much less likely to die. Given access only to other females, eight percent died, while none died among those who had good times with the males and wound up preggers.
Animals that didn't die still developed toxicity, but the dramatic reduction in lethality makes it clear that the toxicity was greatly reduced among those with access to sex.
Agduhr speculated that part of vitamin D's toxicity related to its estrogenic activity. Vitamin D caused abnormalities in the thyroid, parathyroid, pitiuitary, and genital glands. The changes were more severe in males than in females, and certain aspects of these disturbances were partly reversed in the animals that had access to sex. His explanation, at least as far as it was developed in this paper, is not very convincing, but the reduced lethality of vitamin D among mice with access to sex, especially the males, is remarkable.
Generalizing from mice to men can often be problematic, but these findings seem to indicate that sex protects against vitamin D toxicity. Unfortunately, the results do not make clear how much sex is needed or whether its protective effect is dose-dependent. They tell us little about whether pregnancy is necessary, or whether physical or chemical contraception interfere with the protective effect. For that matter, the effect of allowing the offspring to live once born is also unclear. At the moment, this latter point is largely irrelevant because after-birth abortion is still illegal and not widely practiced. Nevertheless, young men and women at risk of vitamin D toxicity, particularly those who supplement or consume foods that may be subjected to accidental over-fortification, may consider marrying as a form of protection. As Regnerus and Uecker point out in Premarital Sex in America (2011, p 81), married emerging adults report having sex 100 times per year compared to the overall mean in this age group of 59. Given the uncertainties listed above, marriage would seem to increase the likelihood of frequent sex and provide a safer environment for the non-use of contraception.
Bottom line? If you accidentally eat the whole bottle of vitamin D, you have two options: break out the A and K, or break out the Marvin Gaye.