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Increased SHBG Levels: ... This increase in SHBG is beneficial as it reduces the levels of free, biologically active sex hormones like estradiol and testosterone, which are linked to various health risks, including breast cancer in postmenopausal women.
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This is probably not a causal relationship. There is not a plausible reason for an isolated change in the binding protein level to influence free hormone levels after a new steady state is achieved. Reiterating a thought experiment: If you take away half of a person's SHBG along with what's bound to it, what causes a change in free hormone levels? The answer is nothing, because the body measures free hormone levels to regulate these hormones, and they haven't changed.
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Postmenopausal Women: In a study involving overweight/obese postmenopausal women, those who underwent a diet and exercise intervention showed significant increases in SHBG levels compared to controls. The study concluded that sustained weight loss results in reductions in free estradiol and testosterone and increases in SHBG 18 months post-intervention.
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This correlation does not imply causality. Calorie restriction alone suppresses hormone production in the HPT axis. In addition, in women, "insulin resistance or high insulin can stimulate ovarian cells to make more testosterone. That happens with PCOS and menopause."[
R] Losing weight can reduce insulin and therefore testosterone and estradiol as well.
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Body Fat and SHBG Production: The reduction in body fat, particularly abdominal fat, is crucial in influencing SHBG levels. Fat tissue is a significant source of estrogen production post-menopause, and its reduction leads to lower estrogen levels and higher SHBG levels.
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This statement is puzzling given that estrogens tend to increase SHBG. In accordance with the previous quote, it may actually be a reduction in testosterone that's driving this. We've seen that testosterone has a stronger influence on SHBG than the estrogen formed from it via aromatization. Alternatively, referencing the OP, there is a negative association between leptin and SHBG. However, so far I haven't come across research establishing causality.
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Dietary Influence: Diet composition also plays a role in SHBG levels. For example, a low-fat diet has been shown to increase SHBG levels, while a high-fat diet decreases them. This suggests that dietary modifications, along with weight loss, can further influence SHBG concentrations.
This review article downplays the influence of diet on SHBG and attributes the bulk of the effect to weight loss.
Reduced caloric intake leading to significant weight loss increases SHBG levels regardless of diet composition, particularly in women. Cross-sectional studies show that dietary composition is generally not associated with SHBG levels independent of obesity level.
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Health Implications
- Breast Cancer Risk: Increased SHBG levels due to weight loss are associated with a reduced risk of estrogen-sensitive breast cancers in postmenopausal women. This is because higher SHBG levels result in lower levels of free estradiol, which is linked to breast cancer risk.
- Cardiovascular and Metabolic Health: Higher SHBG levels are beneficial for cardiovascular and metabolic health. They are associated with lower risks of conditions like diabetes and cardiovascular diseases, which are prevalent in obese individuals.
In summary, losing body fat significantly increases SHBG levels, which has various health benefits, including reduced risks of breast cancer, diabetes, and cardiovascular diseases. The degree of weight loss and the method (diet vs. exercise) can influence the extent of these changes.
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These statements jump from correlation to causality. It's established that higher SHBG is associated with some good things. But where is the evidence that higher SHBG causes them?