Vitamin A quotes from Ray's favorite physiology book
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@Peatly Yes good point . You would expect the opposite. Not sure why that would be. Can Vitamin A substitute for thyroid hormone ?
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@Mauritio Well, I'm not sure. It does seem to modulate the thyroid but not in the way I had previously understood it. I’m yet to understand the full mechanism by which thyroid deficiency may warrant more vitamin A but I am reading and hope to report back.
The relationship between thyroid disorders and vitamin A.: A narrative minireview
From the article
“Retinoid nutritional status is able to modulate thyroid gland homeostasis. Vitamin A deficiency (VAD) appears to be closely related to thyroid gland impairment, due also to its frequent association with iodine deficiency (ID) (3, 4, 6, 10). Indeed, retinoids seem to play a role in the development and maturation of the thyroid cell phenotype (4).”
“Several animal studies using mouse models have shown that VAD is related to reduced iodine uptake, impaired coupling of iodothyronines, and reduced thyroglobulin synthesis, which can lead to thyroid hypertrophy and goiter and to a decreased intrathyroidal pool of T3 and T4 (10–15). The hypothesis that vitamin A deficiency, in the presence of protein-calorie malnutrition, might impair the glycosylation of thyroglobulin (Tg) was proposed by Ingenbleek Y in 1983 (12).”
“A relatively recent Iranian study by Farhangi et al. observed that, in healthy premenopausal obese and non-obese women, 4 months of VAS was able to reduce TSH and increase T3 levels (possibly due to a hepatic effect on the conversion of thyroid hormones), reducing the risk of subclinical thyroid dysfunction (32).”
For some reason I can't find that first quote in the Constance R. Martin book
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@Peatly Wow , very interesting!
Especially those two quotes:@Peatly said in Vitamin A quotes from Ray's favorite physiology book:
“Several animal studies using mouse models have shown that VAD is related to reduced iodine uptake, impaired coupling of iodothyronines, and reduced thyroglobulin synthesis, which can lead to thyroid hypertrophy and goiter and to a decreased intrathyroidal pool of T3 and T4 (10–15).
@Peatly said in Vitamin A quotes from Ray's favorite physiology book:
“A relatively recent Iranian study by Farhangi et al. observed that, in healthy premenopausal obese and non-obese women, 4 months of VAS was able to reduce TSH and increase T3 levels
Dare to think.
My X:
x.com/Metabolicmonstr -
This study shows that high doses of Vitamin A do lead to hypothyroidism (lowered T3, T4, increased TSH) in a dose-dependant manner.
Now the authors were aware of the pro-thyroid effects Vitamin A has in lower doses, so they wanted to see what higher doses did.
The HED I calculated for the lowest dose was about 30 000 IU per day, so not extremely high, yet it still clearly had a visible anti thyroid effect.
I would have liked to see one with 5 or 10 000 IU, which is a much more realistic dose."It has been known that vitamin A deficiency affects thyroid hormones for many years, resulting in iodine deficiency disorders, while vitamin A supplementation alleviates the risk of subclinical hypothyroidism [23, 24]. Recently, a study has been conducted to investigate the relationship between vitamin A and thyroid function in obese individuals. Vitamin A deficiency is more common in subjects with obesity and is significantly related to thyroid dysfunction. Adequate vitamin A levels improved thyroid function in obese subjects with subclinical hypothyroidism [25]. However, no study has focused on the association between vitamin A overload, thyroid dysfunction, and insulin resistance. Therefore, the current study aimed to investigate the effect of prolonged and high doses of vitamin A on thyroid function and glucose metabolism.
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@Mauritio said in Vitamin A quotes from Ray's favorite physiology book:
“A relatively recent Iranian study by Farhangi et al. observed that, in healthy premenopausal obese and non-obese women, 4 months of VAS was able to reduce TSH and increase T3 levels
@Peatful this is the study that you referenced above, which shows a beneficial effect of 25 000 IU of Retinyl palmitate on thyroid markers, meaning increased T3 and lowered TSH.
Its interesting that the rat study found negative effects and the human study postive effects at a similar dosage.
But since human studies are higher up in the evidence pyramide, I tend to interpret this as Vitamin A beeing good for thyroid in reasonable dosages.The effect was especially pronounced in nonobese individuals where T3 increased by more than 60%!
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"In the vitamin A-deficient rats, the thyroid weight increased and the level of serum thyroxine decreased to one half that of the control rats. Normal thyroid weight and serum thyroxine levels were recovered by the replenishment of retinyl palmitate in the vitamin A-deficient rats. In addition, decreased hormone synthesis was observed in the thyroid glands of the vitamin A-deficient rats."
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@Mauritio said in Vitamin A quotes from Ray's favorite physiology book:
@Mauritio said in Vitamin A quotes from Ray's favorite physiology book:
“A relatively recent Iranian study by Farhangi et al. observed that, in healthy premenopausal obese and non-obese women, 4 months of VAS was able to reduce TSH and increase T3 levels
@Peatful this is the study that you referenced above, which shows a beneficial effect of 25 000 IU of Retinyl palmitate on thyroid markers, meaning increased T3 and lowered TSH.
Its interesting that the rat study found negative effects and the human study postive effects at a similar dosage.
But since human studies are higher up in the evidence pyramide, I tend to interpret this as Vitamin A beeing good for thyroid in reasonable dosages.The effect was especially pronounced in nonobese individuals where T3 increased by more than 60%!
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@Peatful said in Vitamin A quotes from Ray's favorite physiology book:
@Mauritio said in Vitamin A quotes from Ray's favorite physiology book:
@Mauritio said in Vitamin A quotes from Ray's favorite physiology book:
“A relatively recent Iranian study by Farhangi et al. observed that, in healthy premenopausal obese and non-obese women, 4 months of VAS was able to reduce TSH and increase T3 levels
@Peatful this is the study that you referenced above, which shows a beneficial effect of 25 000 IU of Retinyl palmitate on thyroid markers, meaning increased T3 and lowered TSH.
Its interesting that the rat study found negative effects and the human study postive effects at a similar dosage.
But since human studies are higher up in the evidence pyramide, I tend to interpret this as Vitamin A beeing good for thyroid in reasonable dosages.The effect was especially pronounced in nonobese individuals where T3 increased by more than 60%!
Oh yes, I meant @Peatly
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@Mauritio There are huge variations in results for vitamin A studies. I think Dr Peat’s recommendation, which is to be cautious if hypothyroid, seems reasonable. I would like to see that Iranian study replicated elsewhere – especially in regions where Billy Goat is blocking the sun.
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@Peatly said in Vitamin A quotes from Ray's favorite physiology book:
@Mauritio There are huge variations in results for vitamin A studies. I think Dr Peat’s recommendation, which is to be cautious if hypothyroid, seems reasonable. I would like to see that Iranian study replicated elsewhere – especially in regions where Billy Goat is blocking the sun.
Yes, I agree.
What does it have to do with the sun/ Vitamin D? -
@Mauritio said in Vitamin A quotes from Ray's favorite physiology book:
@Peatly said in Vitamin A quotes from Ray's favorite physiology book:
@Mauritio There are huge variations in results for vitamin A studies. I think Dr Peat’s recommendation, which is to be cautious if hypothyroid, seems reasonable. I would like to see that Iranian study replicated elsewhere – especially in regions where Billy Goat is blocking the sun.
Yes, I agree.
What does it have to do with the sun/ Vitamin D?I was under the impression that being exposed to sunlight, for extended periods, increases your vitamin A requirements. I was thinking that if the sun is being blocked this might lower need?
Dr Peat talking about light exposure and vitamin A
This is the dentist Dr Peat mentions in that clip
Emanuel Cheraskin, M.D., D.M.D., late Professor of Oral Medicine at the University of Birmingham, AL.
