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Grapefruit* Quercetin* | |
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Vitamin D | |
| Depletion or interference |
None known |
| Side effect reduction/prevention |
None known |
| Supportive interaction |
None known |
| Reduced drug absorption/bioavailability |
None known |
An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.
Quercetin
Studies have shown that grapefruit juice significantly increases estradiol levels in the
blood.1 2 One of the flavonoids found in grapefruit juice is quercetin.
In a test tube study, quercetin was found to change oestrogen metabolism in human liver cells
in a way that increases estradiol levels and reduces other forms of oestrogen.3
This effect is likely to increase oestrogen activity in the body. However, the levels of
quercetin used to alter oestrogen metabolism in the test tube were much higher than levels
found in the body after supplementing with quercetin.
There is evidence from test tube stuudies that another flavonoid in grapefruit juice, naringenin, also has oestrogenic activity.4 It has yet to be shown that dietary or supplemental levels of quercetin (or naringenin) could create a significant problem.
Vitamin D
In controlled studies, the addition of 300 IU per day of vitamin D3 (cholecalciferol) did not
improve the bone-preserving or fracture-preventing effects of hormone replacement with
estradiol plus a progestin (a synthetic form of progesterone) in postmenopausal women without
osteoporosis.5 6 However, in a
controlled study of osteoporotic women, only those receiving both hormone replacement and
vitamin D had increases in bone density of the hip; no improvement occurred in the hip with
hormones alone.7 More research is needed to determine conclusively when vitamin D
is important to add to hormone replacement.
Grapefruit
In a small, controlled study of women with surgically removed ovaries, estradiol levels in the
blood were significantly higher after estradiol was taken with grapefruit juice than when
estradiol was taken alone.8 These results have been independently
confirmed,9 suggesting that women taking oral estradiol should probably avoid
grapefruit altogether.
1. Schubert W, Cullberg G, Edgar B, Hedner T. Inhibition of 17 beta-estradiol metabolism by grapefruit juice in ovariectomized women. Maturitas 1994;20:155–63.
2. Weber A, Jager R, Borner A, et al. Can grapefruit juice influence ethinylestradiol bioavailability? Contraception 1996;53:41–7.
3. Schubert W, Eriksson U, Edgar B, et al. Flavonoids in grapefruit juice inhibit the in vitro hepatic metabolism of 17 beta-estradiol. Eur J Drug Metab Pharmacokinet 1995;3:219–24.
4. Kuiper GG, Lemmen JG, Carlsson B, et al. Interaction of estrogenic chemicals and phytoestrogens with estrogen receptor beta. Endocrinology 1998;139:4252–63.
5. Komulainen M, Kroger H, Tuppurainen MT, et al. Prevention of femoral and lumbar bone loss with hormone replacement therapy and vitamin D3 in early postmenopausal women: a population-based 5-year randomized trial. J Clin Endocrinol Metab 1999;84:546–52.
6. Komulainen MH, Kroger H, Tuppurainen MT, et al. HRT and Vit D in prevention of non-vertebral fractures in postmenopausal women; a 5 year randomized trial. Maturitas 1998;31:45–54.
7. Tuppurainen MT, Komulainen M, Kroger H, et al. Does vitamin D strengthen the increase in femoral neck BMD in osteoporotic women treated with estrogen? Osteoporos Int 1998;8:32–8.
8. Schubert W, Cullberg G, Edgar B, Hedner T. Inhibition of 17 beta-estradiol metabolism by grapefruit juice in ovariectomized women. Maturitas 1994;20:155–63.
9. Weber A, Jager R, Borner A, et al. Can grapefruit juice influence ethinylestradiol bioavailability? Contraception 1996;53:41–7.
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