Vitamin D insufficiency in New Zealanders during the winter is associated with higher parathyroid hormone concentrations: implications for bone health?

BACKGROUND: Parathyroid hormone concentration (PTH) is elevated in vitamin D insufficiency and when prolonged, this condition leads to reduced bone mass and possibly osteoporosis. The threshold of 25-hydroxyvitamin D above which PTH plateaus, is a criterion often used to define vitamin D adequacy. AIMS: To determine whether the higher rates of vitamin D inadequacy reported in the winter than summer months in New Zealand also result in higher PTH concentrations. Also to explore the relationship between 25-hydroxyvitamin D and PTH concentrations in a New Zealand population to determine if a threshold exists for plasma 25-hydroxyvitamin D concentration. METHODS: Plasma 25-hydroxyvitamin D and PTH concentrations were determined in 342 volunteers living in Invercargill and Dunedin (latitude 45-46 degrees S) in late summer (February) and early spring (October). RESULTS: Mean plasma 25-hydroxyvitamin D concentration was higher in the late summer versus early spring (79 vs 51 nmol/L; p<0.001). The lower plasma 25-hydroxyvitamin D in early spring versus summer was associated with a 0.2 pmol/L (p<0.001) higher PTH concentration. A threshold of 61 nmol/L was estimated for plasma 25-hydroxyvitamin D, above which there was no further decrease in PTH concentration. DISCUSSION: The higher PTH concentration in winter than summer suggests that the low 25-hydroxyvitamin D concentration in the winter months may be having an adverse effect on bone health. Many New Zealanders have 25-hydroxyvitamin D concentrations less than 62 nmol/L, especially in winter. Strategies to improve the vitamin D status of the population such as supplementation and food fortification may be needed.

Very high rates of vitamin D insufficiency in women of child-bearing age living in Beijing and Hong Kong.

We aimed to describe the vitamin D status of young women living in two Chinese cities in the spring--Beijing in the north (latitude 39 degrees north) and Hong Kong (latitude 22 degrees north) in the south. We also examined the relationship between serum 25-hydroxyvitamin D and parathyroid hormone (PTH) concentrations to determine a threshold for serum 25-hydroxyvitamin D above which there is no further suppression of PTH. Finally, we examined whether dietary Ca intake influences this relationship. Non-pregnant women aged 18-40 years (n 441) were recruited between February and June. Fasting blood was collected and dietary intakes were assessed using 5 d food records. Mean serum 25-hydroxyvitamin D concentration was lower in Beijing than Hong Kong women (29 v. 34 nmol/l; P < 0.001). Vitamin D deficiency (< or = 25 nmol/l) was indicated in 40% of Beijing and 18% of Hong Kong women, and over 90% of women in both cities were insufficient (< or = 50 nmol/l). Mean Ca and vitamin D intakes were 478 mg/d and 2.0 microg/d, respectively. The relationship between 25-hydroxyvitamin D concentration and PTH was linear throughout the range with a slope of -0.36 (different from 0; P < 0.001; R 0.26), with no apparent threshold. There was no influence of Ca intake on the relationship between 25-hydroxyvitamin D and PTH concentration. Vitamin D deficiency is common and insufficiency is very common in non-pregnant women in Hong Kong and Beijing during spring. Serum 25-hydroxyvitamin D was inversely associated with PTH with no apparent threshold. Strategies such as vitamin D fortification or supplementation may be required.

Folic acid fortified milk increases blood folate and lowers homocysteine concentration in women of childbearing age.

Daily consumption of 400 microg folic acid prior to conception and during early pregnancy is recommended for the prevention of neural tube defects (NTD). Strategies to increase folic acid consumption include supplements and fortified foods. Milk is consumed by women and can be fortified with folic acid but little is known about the effect of fortified milk on blood folate concentration in women of childbearing age. The objective of this study was to determine whether daily consumption of milk fortified with 375 microg folic acid increases blood folate and lowers homocysteine concentrations in women of childbearing age. Seventy-three non-pregnant women (aged 18-47 y) were randomized to receive either 75 g/d of a fortified or unfortified (control) milk powder for 12 weeks. Women who consumed the folic acid fortified milk had mean (95% CI) red blood cell and plasma folate concentrations that were 539 nmol/L (436, 641) and 35 nmol/L (30, 41) higher, respectively, than in the control group. Women drinking fortified milk had a 14% lower mean plasma homocysteine concentration at week 12 than women consuming the control milk. Daily consumption of fortified milk powder providing 375 microg folic acid increases blood folate and lowers homocysteine concentrations over 12 weeks in women of childbearing age. Daily consumption of fortified milk would be expected to reduce NTD risk.

Children who avoid drinking cow's milk are at increased risk for prepubertal bone fractures.

The full fracture histories of 50 children (30 girls and 20 boys, age range 3 to 13 years) who had avoided drinking cow's milk for prolonged periods were compared with those in a birth cohort of more than 1,000 children from the same city. Children who avoided milk did not use calcium-rich food substitutes appropriately and had low dietary calcium intakes and low bone mineral density values. Many were overweight (22 of 50). Significantly more of the children who avoided milk reported fractures (16 observed vs 6 expected, chi(2)=31.0, P<.001, df=5). They also experienced more total fractures than the birth cohort population (22 observed vs 8 expected, chi(2)=33.6, P<.001, df=5). All of the fractures occurred before puberty, the majority (18 of 22) being associated with only slight trauma. Forearm fractures were especially common (12 fractures). We conclude that young children avoiding milk are prone to fracture.