| dc.description.abstract | As a chronic skin disease, plaque psoriasis can cause significant psychosocial, emotional and
physical burden. Psoriasis sufferers perceive others as lacking understanding around what it is
like to live with this condition, and there has been little research exploring the experience of
psoriasis in depth. The burden of psoriasis can be compounded by the difficulty of treating it,
and the inconveniences, side effects and risks of available treatments, suggesting the importance
of finding a safe, effective and convenient treatment for psoriasis. Vitamin D and psoriasis
have a long-standing relationship, with topical vitamin D analogues used to treat mild-tomoderate
disease, and observational studies suggesting an association between higher systemic
vitamin D (serum calcidiol) concentrations and less severe psoriasis. These findings suggest
vitamin D3 supplements, which raise serum calcidiol concentrations, might improve psoriasis.
In this thesis, two studies were conducted to address the limited in-depth understanding of the
experience of psoriasis, and the need for a safe, effective treatment, respectively. The aims
were 1) to gain a deeper understanding of the experience of living with psoriasis; and 2) to
investigate whether oral vitamin D3 supplements can effectively treat psoriasis.
For 1), data from semi-structured interviews with 10 men and women with psoriasis was
analysed using narrative analysis. Narrative trajectories involving three predominant narrative
forms shaped participants’ stories: restitution, where the focus was on overcoming psoriasis
through trying to find an effective treatment or cure; chaos, where psoriasis was experienced as
overwhelming and brought about a sense of hopelessness, and resignation, which was centred
on begrudgingly accepting psoriasis in order to be able to get on with life. Participants had
different narrative trajectories and shifted between forms over time, with the nature of
experience linked with the relative stability and severity of a person’s psoriasis and their beliefs
about their ability to manage it.
For 2), a randomised, double-blinded, placebo-controlled trial was conducted with 101
participants ≥ 18 years allocated to 100,000 International Units (IU) vitamin D3/month (n = 67)
for 12 months (200,000 IU at baseline), or an identical placebo (n = 34). Psoriasis severity
(Psoriasis Area and Severity Index [PASI]) and serum calcidiol concentrations were assessed at
3-monthly intervals. The primary outcome was the difference in PASI between treatment and
placebo over time, assessed using a linear mixed model. Psoriasis severity did not differ
between groups at any time (group F(1, 106) = 0.59, p = 0.44, group*time F(4, 370) = 0.52, p =
0.72). Yet these findings are inconclusive, as serum calcidiol significantly increased from
baseline in both the treatment and the placebo group, and a mild improvement in PASI score
from baseline also occurred in each group. A non-predetermined secondary analysis was
performed by assessing the strength of the relationship between serum calcidiol concentration
and PASI score across the whole sample, and this showed a significant inverse relationship
between the two variables, in that elevation of serum calcidiol concentration by increments from
25 nmol/L to 125 nmol/L was associated with very mild decreases in PASI (estimated range of
decrease 0 – 2.6; p = 0.002). Therefore, despite being unable to determine a benefit of vitamin
D3 supplements for psoriasis, these findings support the notion of a potential benefit of
increasing serum calcidiol concentrations across the psoriatic population.
In conclusion, this thesis offers insight into ways in which people can experience psoriasis over
time: as a temporary and fixable condition that must be overcome, as an overpowering force and
source of significant suffering, and as a permanent condition that is reluctantly accepted. As the
findings emphasise the negative influence of the difficulties around managing and treating
psoriasis on the experience of psoriasis, they provide further support for the need for an
effective, safe and convenient treatment. While the findings were inconclusive in regards to
whether oral vitamin D3 can help people to manage their psoriasis, the significant association
between psoriasis severity and systemic vitamin D concentration supports continued research
into this potential. | en_US |
