As we’ve talked about before, birth control can have some drastic effects on blood biomarkers including sex hormones. If you’ve received your blood test results and been concerned about some elevated (or low) sex hormone markers like DHEAS and SHBG, it’s important to consider how lifestyle factors, like whether you're taking hormonal contraceptives, may play a role. Here's how birth control can affect blood levels of various hormones – and the implications those imbalances have on your health.
A quick recap of the hormones that dictate menstruation
Most hormonal contraceptives are a combination of estrogen and progesterone – two hormones which naturally fluctuate during a monthly menstrual cycle. Their levels help to dictate the maturation and release of an egg and the beginning of menstruation.
Another important, but lesser-acknowledged, hormone in your monthly cycle is testosterone. While often considered only important for males, females also require adequate levels of testosterone in order maintain muscles and bone strength, as well as sex drive and energy levels. Testosterone is the primary androgen in both sexes, but it is found in much lower amounts in females. It is produced by the adrenal glands and sex organs.
Testosterone and sex hormone binding globulin (SHBG)
Testosterone is found as either bound or unbound in the body. Unbound testosterone is considered Free Testosterone. Testosterone that is bound to albumin, a transport protein, is also considered free since it is a relatively weak bind. Surprisingly, only about 3% of testosterone in the body is completely “free”, or unbound, and about 30-35% if bound to albumin. The remaining 70% is bound to sex hormone binding globulin, SHBG.1
How birth control affects SHBG levels
One large meta-analysis found that total testosterone levels can decline by roughly 30%, while free testosterone decline by nearly 60% with the use of hormonal contraceptives. That is a huge reduction! It is thought that it's caused by three mechanisms: 1) the suppression of testosterone production by the ovaries, 2) suppression of testosterone production by the adrenal glands, and 3) increased SHBG levels.1
SHBG rises dramatically with the use of some hormonal birth controls—by as much as 250%.1 SHBG’s exists to bind to sex hormones, making it easier for them to safely travel through the bloodstream. It is produced in the liver in response to testosterone and estrogen, and since hormonal contraceptives typically include a form of estrogen, it makes sense that SHBG levels increase when hormones are added to the body.
Elevated SHBG levels can be alarming, especially without a known explanation. In men, they can be caused by a number of things, such as excessively high levels of testosterone, overtraining, undereating, and inadequate sleep. These things can also impact female’s SHBG levels, but to a drastically lower extent. Usually, in women, hormonal birth control can result in high levels of sex hormone binding globulin.
The critical reason why you should care about this hormone (SHBG)
Like any other medication, taking birth control can have some unintended side effects on other aspects of health. In regards to SHBG, women should be particularly conscious of side effects of birth control because elevated SHBG can be a useful marker to determine the risk for venous thrombosis, or a blood clot.
Now, we don't mean to be alarming, but we fully believe in the fact that “Knowledge is Power.” We want to equip you with the best information for you to make educated decisions about your health. And while use of birth control is a very personal decision, we hope to provide more information about a topic that doesn’t receive the attention it deserves, but affects many—in fact, almost 25% of premenopausal women utilize birth control for family planning, according to the CDC.
Do all forms of birth control affect SHBG the same?
Before tossing your pill pack out the window, know that not all birth controls are created equal. Some cause a much more drastic increase in SHBG levels, while others' impacts are negligible. Overall, IUDs have the lowest impact on SHBG levels. They typically have lower hormone amounts and use of different forms of estrogen and progestin (a synthetic form of progesterone, a hormone that prevents ovulation during pregnancy).
On the other end of the spectrum, hormonal contraceptives in the form of a ring or patch are associated with the highest increase of SHBG levels. Falling somewhere in between are oral contraceptives.
The hormones used also impact the degree of elevation in SHBG. Progestin- or progesterone-only medications are typically associated with the lowest increase in SHBG.3 Levonorgesterel (a synthetic hormone found in many types of contraceptives) is also associated with low impact on SHBG. Perhaps the most used form of estrogen, ethinylestradiol (EE), results in a slight increase. “Low dose” birth controls result in a lower level of elevation than “high dose” options. High dose is typically defined by 50ug of EE or more. Forms including progestogens gestodene, desogestrel, cyproterone acetate, and drospirenone are all associated with higher SHBG levels. Do your research – read the active ingredients of any contraceptives you take to be informed about how they'll affect your SHBG levels. As always, talk to your doctor before changing or stopping any medications you take.
An important recap for making informed birth control decisions
There are many forms of birth control available. Our review does not include every available form, but we do include some of the main ones. In summary. Levonorgesterel, progestin/progesterone, or IUDs appear to have the lowest impact on SHBG levels. Pills containing only levonorgesterel or progestin/progesterone follow, then “low dose” ethinylestradiol. Lastly, high dose ethinylestradiol, the ring, and the patch are associated with the highest increase in SHBG levels.
Impact on SHBG is certainly not the only factor when deciding on a birth control method, but hopefully these insights can help you make a more informed decision or help to explain an elevated SHBG level.
As a part of our on-boarding questionnaire, we ask about hormonal contraceptive use in order to help determine optimal blood biomarker zones and provide the most appropriate recommendations to our users.
Ashley Reaver, MS, RD, CSSD
Ashley is the Lead Nutrition Scientist at InsideTracker. As a registered dietitian and educator, Ashley enjoys cooking and teaching individuals the power that food has on their health. You’ll find Ashley hiking, eating, and spending time with her family. Follow her on Instagram @lower.cholesterol.nutrition.
- Raps, M., Helmerhorst, F., Fleischer, K., Thomassen, S., Rosendaal, F., Rosing, J., Ballieux, B. and Van Vliet, H., 2012. Sex hormone‐binding globulin as a marker for the thrombotic risk of hormonal contraceptives. Journal of Thrombosis and Haemostasis, 10(6), pp.992-997.
- Hugon-Rodin, J., Alhenc-Gelas, M., Hemker, H.C., Brailly-Tabard, S., Guiochon-Mantel, A., Plu-Bureau, G. and Scarabin, P.Y., 2017. Sex hormone-binding globulin and thrombin generation in women using hormonal contraception. Biomarkers, 22(1), pp.81-85.
Some other blog posts we think you'll love: