Hannu Rita

Vitamin D Deficiency and Bone Health in Healthy Adults in Finland: Could This Be a Concern in Other Parts of Europe?

A low vitamin D status could be a concern not only in children and the elderly in Europe, but also in adults. We do not know the effect of mild vitamin D deficiency on bone in this age group. The aim of this study was to detect the prevalence of low serum 25‐hydroxyvitamin D [S‐25(OH)D] and elevated serum intact parathyroid hormone (S‐iPTH) concentrations in healthy young adults in the winter in northern Europe and to characterize the determinants of these variables. In addition, we studied the association between vitamin D status and forearm bone mineral density (BMD) in this population group. Three hundred and twenty‐eight healthy adults (202 women and 126 men, 31–43 years) from southern Finland (60°N) participated in this study conducted in February through March 1998. Fasting overnight blood samples were collected in the morning. Forearm BMD was measured by dual‐energy X‐ray absorptiometry (DXA). The mean daily vitamin D intake met the recommendations in the men (5.6 ± 3.2 μg) and almost met it in the women (4.7 ± 2.5 μg). The mean S‐25(OH)D concentrations did not differ between genders (women, 47 ± 34 nM; men, 45 ± 35 nM; mean ± SD), but the women had significantly higher mean S‐iPTH levels than the men (women, 30 ± 13 ng/liter; men, 24 ± 12 ng/liter; p < 0.001). Low S‐25(OH)D concentrations (<25 nM) were found in 26.2% of the women (53 women) and 28.6% of the men (36 men), respectively. Based on nonlinear regression analysis between S‐25(OH)D and S‐iPTH concentration, the S‐iPTH concentration started to increase with S‐25(OH)D concentrations lower than ∼80 nM in the women and lower than ∼40 nM in the men. Based on this relation between S‐25(OH)D and S‐iPTH concentrations, 86% of the women and 56% of the men had an insufficient vitamin D status. In linear regression analysis, the main positive determinants of S‐25(OH)D were dietary vitamin D intake (p < 0.02), the use of supplements (p < 0.005), alcohol intake (p < 0.05), and age (p < 0.005). Smoking associated negatively with the S‐25(OH)D concentration (p < 0.03). The main determinants of S‐iPTH were S‐25(OH)D (p < 0.01), dietary calcium intake (p < 0.02), and body mass index (BMI; p < 0.01). In addition, female gender was associated with higher S‐iPTH concentration. The mean daily dietary calcium intake was 1037 ± 489 mg and 962 ± 423 mg, in the men and women, respectively. Significantly lower forearm BMD was found in the men (p = 0.01) but not in the women (p = 0.14) with higher S‐iPTH concentrations. Low vitamin D status was prevalent in these young adults in northern Europe in winter, although the vitamin D intake met the recommendation. This probably is not a local problem for northern Europe, because the natural sources of vitamin D are scarce and fortification is not very common in Europe, and with the exception of the southern part of Europe, sunshine is not very abundant in this part of the world. Thus, the results of this study indicate that more attention should be focused on vitamin D status and the sources of vitamin D in these countries.

Competition Versus Cooperation: Success of Individuals Foraging Alone and in Groups

Using a variant of information-sharing models, we examine the pros and cons of group foraging against the alternative of staying alone. Models of this category-assuming that in groups food finding by one results in food sharing by many-conclude that patch-finding rate improves with group size. In our modification interference among individuals reduces pooled searching efficiency of the group. We introduce a term, s, the probability of an individuals being among the ones sharing the food in a patch found by the group. Not unexpectedly, these fine-tunings prolong food-finding rates that push individuals in the group toward the foraging status of a solitary individual. With phenotype-related differences in s, foraging in groups turns out to be a less profitable option the lower an individual is ranked in the group. The model suggests that, in terms of food finding, individuals have to pay attention to their performance in the foraging group. The option of foraging alone may easily be a better strategy than that of a low-ranking individual foraging in a group. If so, the model also suggests groups assorted by phenotype.

Natural regeneration of trees in urban woodlands

Abstract We studied tree regeneration, a key process for the existence of urban woodlands. We hypothesized that, besides the usual biological factors, anthropogenic ones (fragmentation, wear, pollution etc.) determine the regeneration success of tree species in urban woodlands. To test this hypothesis, within an observational setting, we collected data from 30 urban woodlands in the cities of Helsinki and Vantaa, Finland. We defined the number of living saplings (30‐200cm in height) as an indicator of regeneration success and used regression analysis to test different factors as independent variables. The results showed that different tree species responded differently to urban pressure. The regeneration of Picea abies decreased with increasing fragmentation of the forest landscape, whereas for the other most common (deciduous) species, regeneration increased. Wear, measured as total path area per study site, had a negative effect on regeneration success. An a posteriori examination of the data suggested that coarse woody debris might promote regeneration. We conclude that, although tree regeneration in general is not threatened in urban woodlands in the area we studied, the species composition may gradually change. We discuss some management implications for counteracting the urban pressures on tree regeneration. Nomenclature: Hämet‐Ahti et al. 1992.

Low calcium:phosphorus ratio in habitual diets affects serum parathyroid hormone concentration and calcium metabolism in healthy women with adequate calcium intake.

Excessive dietary P intake alone can be deleterious to bone through increased parathyroid hormone (PTH) secretion, but adverse effects on bone increase when dietary Ca intake is low. In many countries, P intake is abundant, whereas Ca intake fails to meet recommendations; an optimal dietary Ca:P ratio is therefore difficult to achieve. Our objective was to investigate how habitual dietary Ca:P ratio affects serum PTH (S-PTH) concentration and other Ca metabolism markers in a population with generally adequate Ca intake. In this cross-sectional analysis of 147 healthy women aged 31-43 years, fasting blood samples and three separate 24-h urinary samples were collected. Participants kept a 4-d food record and were divided into quartiles according to their dietary Ca:P ratios. The 1st quartile with Ca:P molar ratio < or = 0.50 differed significantly from the 2nd (Ca:P molar ratio 0.51-0.57), 3rd (Ca:P molar ratio 0.58-0.64) and 4th (Ca:P molar ratio > or = 0.65) quartiles by interfering with Ca metabolism. In the 1st quartile, mean S-PTH concentration (P = 0.021) and mean urinary Ca (U-Ca) excretion were higher (P = 0.051) than in all other quartiles. These findings suggest that in habitual diets low Ca:P ratios may interfere with homoeostasis of Ca metabolism and increase bone resorption, as indicated by higher S-PTH and U-Ca levels. Because low habitual dietary Ca:P ratios are common in Western diets, more attention should be focused on decreasing excessively high dietary P intake and increasing Ca intake to the recommended level.

Randomized study of the effect of antenatal dexamethasone on growth and development of premature children at the corrected age of 2 years

The objective of the series was to study the effect of prenatal dexamethasone therapy on the growth and neurological development of preterm children until the age of 2 years. Eighty‐two children with a mean gestational age of 30 (24–33) weeks and a mean weight of 1291 (530–2360) g at birth, treated antenatally with either dexamethasone (n= 50) or placebo (n= 32), were examined at the adjusted age of 24 months by a paediatric neurologist, a neuropsychologist and a speech therapist. Neurological development was defined as normal if all scores of neuropaediatric, neuropsychological and verbal tests were within the normal range. Normal neurological development was found in 52% of the dexamethasone‐treated and in 34% of the placebo‐treated children. The incidence of cerebral palsy was 10% in the dexamethasone group and 22% in the placebo group. Minor developmental delay was found in 42% of dexamethasone‐treated and in 53% of placebo‐treated children. Our follow‐up results indicate that the beneficial effect of prenatal glucocorticoid treatment on cerebral complications I intraventricular haemorrhage or periventricular leucomalacia) demonstrated during the neonatal period may be followed by a lower incidence of cerebral palsy in surviving premature children.

Habitual high phosphorus intakes and foods with phosphate additives negatively affect serum parathyroid hormone concentration: a cross-sectional study on healthy premenopausal women.

OBJECTIVE Foods can contain natural phosphorus (NP) and phosphate-containing food additives (AP). The main objective of the present study was to investigate whether NP and AP of habitual diets differ in their effects on markers of Ca metabolism. We also investigated the impact of total habitual dietary P intake on markers of Ca metabolism. DESIGN Cross-sectional study. Fasting blood samples were collected and participants kept a 4 d food record, from which dietary intake of total P and the consumption of NP (milk and cheese, excluding processed cheese) and AP (processed cheese) sources were calculated. Participants were divided into groups according to their NP- and AP-containing food consumption and into quartiles according to their total P intake. SETTING Southern Finland. SUBJECTS One hundred and forty-seven healthy premenopausal women aged 31-43 years. RESULTS Relative to the lowest total dietary P quartile, mean serum parathyroid hormone (S-PTH) concentration was higher (P = 0.048, analysis of covariance (ANCOVA)) and the mean serum ionized Ca concentration lower (P = 0.016, ANCOVA) in the highest P intake quartile. Mean S-PTH concentrations were higher among participants who consumed processed cheese (P = 0.027, ANCOVA) and less milk and other cheese than processed cheese (P = 0.030, ANCOVA). CONCLUSIONS High total habitual dietary P intake affected S-PTH unfavourably. Furthermore, phosphate additives may have more harmful effects on bone than other P sources, as indicated by higher mean S-PTH concentration among participants who consumed AP-containing foods. Because of the high dietary P intake and current upward trend in consumption of processed foods in Western countries, these findings may have important public health implications.

Significance of memory properties in prey choice decisions

Abstract To forage efficiently in a spatially and temporally heterogeneous environment requires that an individual’s information from the immediate past is combined with information from the more distant past to track environmental change. We made use of a model involving exponentially devaluating weights for past events to emulate behaviour of the individual’s memory. As the devaluation rate increases, more weight is given to the most recent events. First, performance of individuals with different memory properties was tested in simulations in which two prey types with different profitabilities were available in different proportions. In a structurally stable prey environment a low memory devaluation rate gave better estimation of prey proportions than a high memory devaluation rate. In a highly variable environment, on the contrary, individuals with high devaluation rate could more quickly correct their estimates as prey availability changed, although this was achieved with the cost of high error rate of the estimate. Second, the ability to reliably assess relative abundances of the prey types proved to increase an individual’s success in prey choice (according to the decision rules by the optimal prey choice model). Third, in further simulations individuals were allowed to adjust their memory devaluation rate according to experience from their success in prey choice decisions in previous patches. We found that there was no need to adjust a high devaluation memory in a highly variable environment, but foragers starting with low devaluation value rather rapidly shifted to high devaluation rates. In a relatively stable environment the situation was reversed and finally all foragers used low devaluation rates. These results imply that the variation in estimation efficacy of prey availability may be critical in terms of optimal prey choice and thus memory properties should be included in examinations of prey choice. Including individual variation in foraging performance in individual-based models could increase our understanding of the consequences of these differences at the population and community levels.

Producers, scroungers and foraging group structure

The producer–scrounger model of Barnard & Sibly (1981,Anim. Behav.,29,543–550) predicts that at a certain ratio of producers and scroungers in a foraging group the payoff curves for individuals of the two phenotypes intercept. At this point all the group members obtain equal payoffs. In this paper, the original model is elaborated further by allowing individuals to differ not only in their food-finding abilities but also in their abilities to compete for the food once it is found. As in Barnard & Siblys original model foraging individuals are assumed to share information about the whereabouts of food patches and to benefit from patches found by others. Here it is determined under which combinations of searching and sharing characters food intake rate in mixed-phenotype groups would be equal for producing and scrounging individuals. In the present model the payoffs are much affected by both the finders advantage (the fraction of prey available only to the finder of the food-patch) and the combination of the foraging characters of the two phenotypes. Generally the intake rate of producers increases with their presence in the group and with increases in the finders advantage. Our model suggests that the equal payoffs arise only when the relative food-searching and competitive abilities of producers and scroungers fall within a narrow range of options acknowledging also the finders advantage. Moreover, such combinations are predicted to be unstable if only foraging benefits are called for in group formation, this being a common feature of social foraging models incorporating foraging role asymmetries.

Wintertime Vitamin D Supplementation Inhibits Seasonal Variation of Calcitropic Hormones and Maintains Bone Turnover in Healthy Men

Vitamin D is suggested to have a role in the coupling of bone resorption and formation. Compared with women, men are believed to have more stable bone remodeling, and thus, are considered less susceptible to the seasonal variation of calcitropic hormones. We examined whether seasonal variation exists in calcitropic hormones, bone remodeling markers, and BMD in healthy men. Furthermore, we determined which vitamin D intake is required to prevent this variation. Subjects (N = 48) were healthy white men 21–49 yr of age from the Helsinki area with a mean habitual dietary intake of vitamin D of 6.6 ± 5.1 (SD) μg/d. This was a 6‐mo double‐blinded vitamin D intervention study, in which subjects were allocated to three groups of 20 μg (800 IU), 10 μg (400 IU), or placebo. Fasting blood samplings were collected six times for analyses of serum (S‐)25(OH)D, iPTH, bone‐specific alkaline phosphatase (BALP), and TRACP. Radial volumetric BMD (vBMD) was measured at the beginning and end of the study with pQCT. Wintertime variation was noted in S‐25(OH)D, S‐PTH, and S‐TRACP (p < 0.001, p = 0.012, and p < 0.05, respectively) but not in S‐BALP or vBMD in the placebo group. Supplementation inhibited the winter elevation of PTH (p = 0.035), decreased the S‐BALP concentration (p < 0.05), but benefited cortical BMD (p = 0.09) only slightly. Healthy men are exposed to wintertime decrease in vitamin D status that impacts PTH concentration. Vitamin D supplementation improved vitamin D status and inhibited the winter elevation of PTH and also decreased BALP concentration. The ratio of TRACP to BALP shows the coupling of bone remodeling in a robust way. A stable ratio was observed among those retaining a stable PTH throughout the study. A daily intake of vitamin D in the range of 17.5–20 μg (700–800 IU) seems to be required to prevent winter seasonal increases in PTH and maintain stable bone turnover in young, healthy white men.

Female characteristics and parental care mode in the creching system of eiders, Somateria mollissima

Eider females may abandon their young, care alone, or join in multifemale creches. We studied the characteristics of female eiders adopting these strategies in 1996-1999. Female condition at hatching varied significantly between years. Over all years, 31% of all females abandoned, 23% tended alone and 46% creched. In the year when average female condition at hatching was lowest, abandonment rate peaked (67%). Creching birds were further identified as true crechers staying more than 2 weeks with the original creche, and transient crechers leaving the creche. The condition of females shortly before hatching showed a decreasing trend, with lone tenders being in best condition, followed by true crechers, transient crechers and abandoners. Clutch size, date of hatching relative to the population median, and female body size did not differ between groups. Individual females switched between care modes between years. Females weighed significantly less when abandoning than when tending, with no significant weight difference when the females remained as tenders between 2 years. This is consistent with the energetic salvage strategy hypothesis, which states that females in poor body condition should be more prone to abandon their brood. Our results support an adaptive approach to offspring care behaviour in eiders, driven by female condition.  2001 The Association for the Study of Animal Behaviour