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Healthy elderly French women living at home have secondary hyperparathyroidism and high bone turnover in winter. EPIDOS Study Group. Chapuy MC, Schott AM, Garnero P, Hans D, Delmas PD, Meunier PJ. J Clin Endocrinol Metab. 1996 Mar;81(3):1129-33. PMID: 8772587 These results show that vitamin D status of a French aged population in good health and living at home depends mainly on lifestyle. Like institutionalized women, old women living at home exhibit clear evidence of senile hyperparathyroidism in the winter, secondary in part to a reduced 25OHD level and associated with biological signs of increased bone turnover. The maintenance of PTH within the normal range for healthy adults by vitamin D and calcium treatment might constitute an approach for the prevention of bone loss in the entire

25(OH)D Serum levels decline with age earlier in women than in men and less efficiently prevent compensatory hyperparathyroidism in older adults. Maggio D, Cherubini A, Lauretani F, Russo RC, Bartali B, Pierandrei M, Ruggiero C, Macchiarulo MC, Giorgino R, Minisola S, Ferrucci L. J Gerontol A Biol Sci Med Sci. 2005 Nov;60(11):1414-9. PMID: 16339327 Conclusions. These findings suggest that the age-associated fall of serum 25(OH)D starts earlier in women than in men and that higher levels of 25(OH)D are required in older compared to younger persons to avoid the age-associated compensatory hyperparathyroidism.

Age-related changes in the 25-hydroxyvitamin D versus parathyroid hormone relationship suggest a different reason why older adults require more vitamin D. Vieth R, Ladak Y, Walfish PG. J Clin Endocrinol Metab. 2003 Jan;88(1):185-91. PMID: 12519850 This study shows that all age groups exhibit a high prevalence of 25(OH)D insufficiency and secondary hyperparathyroidism. Older adults are just as efficient in maintaining 25(OH)D, but they need more vitamin D to produce the higher 25(OH)D concentrations required to overcome the hyperparathyroidism associated with their diminishing renal function

Low serum 25-hydroxyvitamin D concentrations and secondary hyperparathyroidism in middle-aged white strict vegetarians. Lamberg-Allardt C, Kärkkäinen M, Seppänen R, Biström H. Am J Clin Nutr. 1993 Nov;58(5):684-9. PMID: 8237875 In conclusion, white strict vegetarians are at risk of vitamin D deficiency, at least in the winter, primarily because of a low dietary vitamin D intake, despite a normal sunlight exposure in summer. Low serum 25(OH)D concentrations are accompanied by high S-iPTH concentrations, which also are affected by a low calcium intake. The effect of these changes on bone health remains to be evaluated.

Unusually prolonged vitamin D intoxication after discontinuation of vitamin D: possible role of primary hyperparathyroidism. Taskapan H, Vieth R, Oreopoulos DG. Int Urol Nephrol. 2008;40(3):801-5. Epub 2008 Jun 5. PMID: 18528779 DOI: 10.1007/s11255-008-9404-1

Association of low 25-hydroxyvitamin D concentrations with elevated parathyroid hormone concentrations and low cortical bone density in early pubertal and prepubertal Finnish girls. Cheng S, Tylavsky F, Kröger H, Kärkkäinen M, Lyytikäinen A, Koistinen A, Mahonen A, Alen M, Halleen J, Väänänen K, Lamberg-Allardt C. Am J Clin Nutr. 2003 Sep;78(3):485-92. Erratum in: Am J Clin Nutr. 2006 Jan;83(1):174. PMID: 12936933 CONCLUSIONS: Vitamin D-deficient girls have low cortical BMD and high iPTH concentrations, which are consistent with secondary hyperparathyroidism. A low vitamin D concentration accompanied by high bone resorption (TRAP 5b) may limit the accretion of bone mass in young girls.

A high prevalence of hypovitaminosis D in Finnish medical in- and outpatients. Kauppinen-Mäkelin R, Tähtelä R, Löyttyniemi E, Kärkkäinen J, Välimäki MJ. J Intern Med. 2001 Jun;249(6):559-63. PMID: 11422663 DOI: 10.1046/j.1365-2796.2001.00847.x CONCLUSION: Hypovitaminosis D is very common amongst Finnish in- and outpatients in both sexes, causing secondary hyperparathyroidism in females. More extensive studies are warranted to elucidate the vitamin D status of the Finnish population.

Vitamin D is safe when used in physiological doses (those used by Nature). Physiological doses are 3,000-5,000 IU/day, from all sources (sun, diet and supplements). Should hypercalcemia occur with such doses, it is due to vitamin D hypersensitivity syndrome, not vitamin D toxicity. Vitamin D hypersensitivity syndromes include conditions such as primary hyperparathyroidism, occult cancers (especially lymphoma) or granulomatous disease (especially sarcoidosis). In such cases, treatment of vitamin D deficiency should be done under the care of a knowledgeable physician. A serum 25(OH)D, serum 1,25(OH)D, PTH and SMA will lead the clinician in the right direction.

Evidence for alteration of the vitamin D-endocrine system in obese subjects. Bell NH, Epstein S, Greene A, Shary J, Oexmann MJ, Shaw S. J Clin Invest. 1985 Jul;76(1):370-3. PMID: 2991340 The results provide evidence that alteration of the vitamin D-endocrine system in obese subjects is characterized by secondary hyperparathyroidism which is associated with enhanced renal tubular reabsorption of calcium and increased circulating 1,25(OH)2D. The reduction of serum 25-OHD in them is attributed to feedback inhibition of hepatic synthesis of the precursor by the increased serum 1,25(OH)2D.

Low vitamin D status, high bone turnover, and bone fractures in centenarians. Passeri G, Pini G, Troiano L, Vescovini R, Sansoni P, Passeri M, Gueresi P, Delsignore R, Pedrazzoni M, Franceschi C. J Clin Endocrinol Metab. 2003 Nov;88(11):5109-15. PMID: 14602735 We conclude that the extreme decades of life are characterized by a pathophysiological sequence of events linking vitamin D deficiency, low serum calcium, and secondary hyperparathyroidism with an increase in bone resorption and severe osteopenia. These data offer a rationale for the possible prevention of elevated bone turnover, bone loss, and consequently the reduction of osteoporotic fractures and fracture-induced disability in the oldest olds through the supplementation with calcium and vitamin D.

"Hypervitaminosis D is a state of vitamin D toxicity. The recommended daily allowance is 400 IU per day. Overdose has been observed at 1925 µg/d (77,000 IU per day). Acute overdose requires between 15,000 µg/d (600,000 IU per day) and 42,000 µg/d (1,680,000 IU per day) over a period of several days to months, with a safe intake level being 250 µg/d (10,000 IU per day).[1] Foods contain low levels, and have not been known to cause overdose. Overdose has occurred due to industrial accidents, for example when incorrectly formulated pills were sold or missing industrial concentrate cans misused as cans of milk. Vitamin D toxicity is unlikely except when certain medical conditions are present, such as primary hyperparathyroidism, sarcoidosis, tuberculosis, and lymphoma."

Vieth R.Vitamin D supplementation, 25-hydroxyvitamin D concentrations, andsafety.Am J Clin Nutr. 1999 May;69(5):842-56. Review.PMID: 10232622