Caster Semenya: Does limiting testosterone in female athletes make sport fairer? © Getty Images

Caster Semenya: Will limiting testosterone in female athletes make sport fairer?

The Olympic gold medallist Caster Semenya's naturally high testosterone levels are said to give her an athletic advantage, but is this really the case? Professor Peter Sonksen, OBE, and Professor Malcolm Ferguson-Smith think not.

Updated 02/05/19: Since this article was first published, Semenya has lost her appeal and must artificially lower her testosterone levels to compete in events from 8 May 2019 onwards. Professor Sonksen and Professor Ferguson-Smith have provided the following comment on the ruling:

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It is clear that the 2:1 split within Cas reflects the difficulty they had in making a decision in this case; however, as the proverb states, the proof of the pudding will be in the eating… If Caster can find an oral contraceptive pill that does suppress her endogenous testosterone to meet the IAAF requirements without upsetting her and yet she continues winning (as we forecast) then Q.E.D. – her case is proven.

On the other hand, making her take medication for non-medical reasons remains unethical.

We are also concerned about bias and the IAAF definition of ‘androgen sensitive female’ since Caster Semenya, like Dutee Chand must be severely androgen insensitive since they were born normal female babies and have normal female bodies and were only diagnosed DSD on a blood test done when adults. Thus, in our eyes, they are already proven to be androgen insensitive and should be allowed to compete in any event.

The original article begins below.


Caster Semenya, the South African athlete and Olympic gold medallist, has been embroiled in controversy for much of her career over her higher than usual testosterone level, a disorder of sex development (DSD) known as hyperandrogenism.

Semenya and her team of legal, medical and scientific advisors have recently been at the Court of Arbitration for Sport (CAS) in Lausanne, appealing the new rule proposed by the International Association of Athletics Federations (IAAF), the governing body for athletics, that prevents female athletes with hyperandrogenism from competing in events from 400 metres to 1 mile if their testosterone level is above 5 nanomoles per litre.

For comparison, South Tees Hospitals NHS Foundation Trust gives reference ranges for testosterone levels of 0.7 to 2.8 nanomoles per litre in women, and 10 to 30 nanomoles per litre in men. The IAAF are arguing that women with hyperandrogenism have a physically-enhanced athletic ability. This conclusion is strongly challenged.

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Quite rightly, we do not know the details of Caster’s medical record other that she was born and raised as a normal female baby, infant and girl and went on to become a very talented and gifted woman athlete.

As a result of blood tests, she was found to have a high testosterone level that was above that usually seen in women. The IAAF and their advisors (incorrectly) attribute her athletic success to the effects of the high testosterone and hence require her to lower it, through pharmacological or surgical means, to less than 5 nanomoles per litre to be eligible to compete in these events.

The IAAF had an earlier version of this rule suspended by CAS in July 2015 as the result of a successful appeal by the Indian athlete Dutee Chand, citing a lack of evidence. The court gave the IAAF two years to come back to them with convincing evidence to support their case.

Rather than meet the CAS requirements, the IAAF chose to bypass this by proposing a new variation on the rule that did not exclude Chand from her events but appeared to target events favoured by Semenya. This rule is based on a 2017 IAAF-funded study which claimed to find an athletic advantage based solely on testosterone levels. Amanda Menier of the University of Massachusetts Amherst, among others, criticised the conclusions drawn by this study.

Silver medalist Dutee Chand of India poses for photo during Athletics WomenÕs 200m medal ceremony at GBK Main Stadium on day eleven of the Asian Games on August 29, 2018 in Jakarta, Indonesia. (Photo by Yifan Ding/Getty Images)
Dutee Chand of India © Yifan Ding/Getty Images

Despite a lack of detail of her medical record, it seems most likely that Semenya has Androgen Insensitivity Syndrome (AIS). A developing foetus with AIS, although being genetically male with XY chromosomes and testes, does not respond to the male testosterone levels because of a defect in the testosterone receptor gene. As a result, the infant is female at birth and develops as a normal girl and then woman.

The diagnosis is often not made until the (adult) woman fails to menstruate or proves infertile and then seeks medical advice. In Semenya’s case, as with Chand, the diagnosis was likely made after the routine anti-doping test found her high testosterone level.

Some cases of AIS have less severe androgen insensitivity and are diagnosed at birth because of ambiguous genitalia. These are known as ‘partial’ or ‘incomplete’ AIS. Although they are testosterone resistant, they are still able to respond partially, and hence develop genitalia that is incompletely masculinised. This is quite distinct from the cases of Semenya and Chand, who were born female and raised as women. Whatever the exact genetic cause, they are both severely insensitive to testosterone.

This is the crux of the argument and one that the IAAF choose to avoid. Women with AIS cannot respond to injected testosterone, so it would be no use to them as a doping agent. In fact, many have had their testes removed and despite zero testosterone levels managed to qualify for the Olympic Games.

Read more:

Professor Malcolm Ferguson-Smith, of the Cambridge Resource Centre for Comparative Genomics, and colleagues tested 3,387 women athletes at the Atlanta Olympic Games and found eight with XY sex chromosomes, of whom seven had AIS. Their heights were in the normal male range. Six of them had already had a gonadectomy and despite this were able to reach Olympic standard. In other words, virtually complete lack of testosterone did not appear to affect their athletic performance.

In a subsequent paper, Ferguson-Smith found that genes on the Y chromosome, especially those genes associated with height in the male range, are the most likely explanation for the high number of XY women with AIS and other DSDs in elite sport, rather than testosterone levels.

All athletes are selected largely on their inherent, physical attributes due to their genetic constitution. Favourable genes on many chromosomes are known to be involved and it is discriminatory to exclude those athletes who have favourable genes on the Y chromosome.

These athletes with AIS are at no greater advantage than those who are selected because of favourable genes on other chromosomes. As Ferguson-Smith explains, “women with hyperandrogenism possess no physical attribute relevant to athletic performance that is neither attainable, nor present in other women.”

Thus, the IAAF are ‘barking up the wrong tree’ medically (and ethically) by unfairly attempting to exclude women with AIS from elite sport. Let us hope that CAS do not fall into the same trap.

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