Background
Severe vitamin D deficiency causes osteomalacia, yet trials of vitamin D supplementation in the community have not on average demonstrated benefit to bone mineral density (BMD) or fracture ...risk in adults.
Objective
To determine whether monthly high‐dose vitamin D supplementation influences BMD in the general population and in those with low 25‐hydroxyvitamin D levels.
Methods
Two‐year substudy of a trial in older community‐resident adults. A total of 452 participants were randomized to receive monthly doses of vitamin D3 100 000 IU, or placebo. The primary end‐point was change in lumbar spine BMD. Exploratory analyses to identify thresholds of baseline 25‐hydroxyvitamin D for vitamin D effects on BMD were prespecified.
Results
Intention‐to‐treat analyses showed no significant treatment effect in the lumbar spine (between‐groups difference 0.0071 g cm−2, 95%CI: −0.0012, 0.0154) or total body but BMD loss at both hip sites was significantly attenuated by ~1/2% over 2 years. There was a significant interaction between baseline 25‐hydroxyvitamin D and treatment effect (P = 0.04). With baseline 25‐hydroxyvitamin D ≤ 30 nmol L−1 (n = 46), there were between‐groups BMD changes at the spine and femoral sites of ~2%, significant in the spine and femoral neck, but there was no effect on total body BMD. When baseline 25‐hydroxyvitamin D was >30 nmol L−1, differences were ~1/2% and significant only at the total hip.
Conclusions
This substudy finds no clinically important benefit to BMD from untargeted vitamin D supplementation of older, community‐dwelling adults. Exploratory analyses suggest meaningful benefit in those with baseline 25‐hydroxyvitamin D ≤ 30 nmol L−1. This represents a significant step towards a trial‐based definition of vitamin D deficiency for bone health in older adults.
Click here to view the Editorial Comment by R. Bouillon.
Background
We recently reported that the administration of zoledronate every 18 months to osteopenic older women reduces the incidence of fractures.
Objective
Here, we present a more detailed ...analysis of that trial to determine whether baseline clinical characteristics impact on the anti‐fracture efficacy of this intervention.
Methods
This is a prospective, randomized, placebo‐controlled, double‐blind trial in osteopenic postmenopausal women aged ≥ 65 years, to determine the anti‐fracture efficacy of zoledronate. 2000 women were recruited using electoral rolls and randomized to receive 4 infusions of either zoledronate 5 mg or normal saline, at 18‐month intervals. Each participant was followed for 6 years. Calcium supplements were not supplied.
Results
Fragility fractures (either vertebral or nonvertebral) occurred in 190 women in the placebo group (227 fractures) and in 122 women in the zoledronate group (131 fractures), odds ratio (OR) 0.59 (95%CI 0.46, 0.76; P < 0.0001). There were no significant interactions between baseline variables (age, anthropometry, BMI, dietary calcium intake, baseline fracture status, recent falls history, bone mineral density, calculated fracture risk) and the treatment effect. In particular, the reduction in fractures appeared to be independent of baseline fracture risk, and numbers needed to treat (NNT) to prevent one woman fracturing were not significantly different across baseline fracture risk tertiles.
Conclusions
The present analyses indicate that the decrease in fracture numbers is broadly consistent across this cohort. The lack of relationship between NNTs and baseline fracture risk calls into question the need for BMD measurement and precise fracture risk assessment before initiating treatment in older postmenopausal women.
Zoledronate prevented fractures in osteopenic women aged >65 years, and this was independent of baseline characteristics such as age, history of fractures and falls, and calculated fracture risk.
Abstract
We present an analysis of the
BVRI
photometry of the blazar BL Lacertae on diverse timescales from 2020 mid-July to mid-September. We have used 11 different optical telescopes around the ...world and have collected data over 84 observational nights. The observations cover the onset of a new activity phase of BL Lacertae that started in 2020 August (termed as the 2020 August flare by us), and the analysis is focused on the intranight variability. On short-term timescales, (i) flux varied with ∼2.2 mag in the
R
band, (ii) the spectral index was found to be weakly dependent on the flux (i.e., the variations could be considered mildly chromatic), and (iii) no periodicity was detected. On intranight timescales, BL Lacertae was found to predominantly show bluer-when-brighter chromatism. We also found two cases of significant interband time lags of the order of a few minutes. The duty cycle of the blazar during the 2020 August flare was estimated to be quite high (∼90% or higher). We decomposed the intranight light curves into individual flares and determined their characteristics. On the basis of our analysis and assuming the turbulent jet model, we determined some characteristics of the emitting regions: Doppler factor, magnetic field strength, electron Lorentz factor, and radius. The radii determined were discussed in the framework of the Kolmogorov theory of turbulence. We also estimated the weighted mean structure function slope on intranight timescales, related it to the slope of the power spectral density, and discussed it with regard to the origin of intranight variability.
ABSTRACT
We have monitored the flat spectrum radio quasar, 3C 279, in the optical B, V, R, and I passbands from 2018 February to 2018 July for 24 nights, with a total of 716 frames, to study flux, ...colour, and spectral variability on diverse time-scales. 3C 279 was observed using seven different telescopes: two in India, two in Argentina, two in Bulgaria, and one in Turkey to understand the nature of the source in optical regime. The source was found to be active during the whole monitoring period and displayed significant flux variations in B, V, R, and I passbands. Variability amplitudes on intraday basis varied from 5.20 to 17.9 per cent. A close inspection of variability patterns during our observation cycle reveals simultaneity among optical emissions from all passbands. During the complete monitoring period, progressive increase in the amplitude of variability with frequency was detected for our target. The amplitudes of variability in B, V, R, and I passbands have been estimated to be 177 per cent, 172 per cent, 171 per cent, and 158 per cent, respectively. Using the structure function technique, we found intraday time-scales ranging from ∼23 min to about 115 min. We also studied colour–magnitude relationship and found indications of mild bluer-when-brighter trend on shorter time-scales. Spectral indices ranged from 2.3 to 3.0 with no clear trend on long-term basis. We have also generated spectral energy distributions for 3C 279 in optical B, V, R, and I passbands for 17 nights. Finally, possible emission mechanisms causing variability in blazars are discussed briefly.
We present the results of extensive multiband intranight optical monitoring of BL Lacertae during 2010–2012. BL Lacertae was very active in this period and showed intense variability in almost all ...wavelengths. We extensively observed it for a total for 38 nights; on 26 of them, observations were done quasi-simultaneously in B, V, R and I bands (totalling 113 light curves), with an average sampling interval of around 8 min. BL Lacertae showed significant variations on hour-like time-scales in a total of 19 nights in different optical bands. We did not find any evidence for periodicities or characteristic variability time-scales in the light curves. The intranight variability amplitude is generally greater at higher frequencies and decreases as the source flux increases. We found spectral variations in BL Lacertae in the sense that the optical spectrum becomes flatter as the flux increases but in several flaring states, deviates from the linear trend suggesting different jet components contributing to the emission at different times.
We report the results of quasi-simultaneous two-filter optical monitoring of two high-energy peaked blazars, 1ES 1959+650 and 1ES 2344+514, to search for microvariability and short-term variability ...(STV). We carried out optical photometric monitoring of these sources in an alternating sequence of B and R passbands, and have 24 and 19 nights of new data for these two sources, respectively. No genuine microvariability (intranight variability) was detected in either of these sources. This non-detection of intranight variations is in agreement with the conclusions of previous studies that high-energy peaked BL Lacs are intrinsically less variable than low-energy peaked BL Lacs in the optical bands. We also report the results of STV studies for these two sources between 2009 July and 2010 August. Genuine STV is found for the source 1ES 1959+650 but not for 1ES 2344+514. We briefly discuss possible reasons for the difference between the intranight variability behaviour of high- and low-energy peaked blazars.
Optical flux and spectral variability of blazars Gaur, Haritma; Gupta, Alok C.; Strigachev, A. ...
Monthly notices of the Royal Astronomical Society,
1 October 2012, 20121001, Letnik:
425, Številka:
4
Journal Article
Recenzirano
ABSTRACT
We report the results of optical monitoring for a sample of 11 blazars including 10 BL Lacertae objects (BL Lacs) and one flat spectrum radio quasar (FSRQ). We have measured the multiband ...optical flux and colour variations in these blazars on intraday and short‐term time‐scales of months and have limited data for two more blazars. These photometric observations were made during 2009–2011, using six optical telescopes, four in Bulgaria, one in Greece and one in India. On short‐term time‐scales we found significant flux variations in nine of the sources and colour variations in three of them. Intraday variability was detected on six nights for two sources out of the 18 nights and four sources for which we collected such data. These new optical observations of these blazars plus data from our previous published papers (for three more blazars) were used to analyse their spectral flux distributions in the optical frequency range. Our full sample for this purpose includes six high‐synchrotron‐frequency‐peaked BL Lacs (HSPs), three intermediate‐synchrotron‐frequency‐peaked BL Lacs (ISPs) and six low‐synchrotron‐frequency‐peaked BL Lacs (LSPs; including both BL Lacs and FSRQs). We also investigated the spectral slope variability and found that the average spectral slopes of LSPs show a good accordance with the synchrotron self‐Compton loss dominated model. Our analysis supports previous studies that found that the spectra of the HSPs and FSRQs have significant additional emission components. The spectra of all these HSPs and LSPs get flatter when they become brighter, while for FSRQs the opposite appears to hold. This supports the hypothesis that there is a significant thermal contribution to the optical spectrum for FSRQs.
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