Vitamin D Supplementation May Have The Potential To Increase Life Expectancy
Vitamin D is known as the "sunshine vitamin" as it is synthesised in the skin upon exposure to ultraviolet-B (UVB) radiation from sunlight; it is a fat soluble vitamin most famous for its role in preventing rickets in children.
The circulating form of the vitamin is 25-hydroxyvitamin D, the active form of the vitamin is 1, 25-dihydroxyvitamin D (1,25(OH)2D). When blood calcium levels fall low parathyroid hormone (PTH) is secreted; this stimulates increased production of active vitamin D, which acts to increase the absorption of calcium. In vitamin D deficiency, calcium absorption is insufficient to satisfy the body's calcium needs, consequently PTH production is increased and calcium is drawn from the skeleton to maintain normal blood calcium levels, with devastating consequences for bone health. Recent evidence however suggests that the role of vitamin D is far more complex and vital than maintaining calcium levels.
More than 50 genes in tissues throughout the body are known to be regulated by 1,25(OH)2D. Vitamin D deficiency may contribute to conditions such as cancer, hypertension, insulin resistance and poor immunity. Two new studies have indicated that optimal vitamin D status may increase life expectancy.
Vitamin D & Life Expectancy Among The Elderly
In this study data was analysed from 567 men and women aged 75 and over who were monitored over a 17 year period. Accounting for factors such as age and gender, high blood levels of PTH (a measure of vitamin D deficiency as the body attempts to increase calcium levels) were associated with a 24% increased risk of death and an average reduction in life expectancy of 2.3 years. The tendency for increased mortality was consistent in both genders, in all age groups as well as in subjects with varying co-morbidity, renal function, body mass index categories and calcium levels. The authors concluded: "Elevated serum PTH level is an independent predictor of impaired long-term survival prognosis in unselected aged population. The long-term prognostic impact of vitamin D deficiency, the most common cause of elevated PTH levels in the elderly, remains to be investigated."
Click here to view the study abstract.
Vitamin D & All-Cause & Cardiovascular Mortality
This study sought to uncover any association between low 25(OH)D levels and all-cause, cancer, and cardiovascular disease (CVD) mortality. Data was analysed from 13,331 nationally representative adults 20 years or older. Those categorised as having the lowest levels of 25-hydroxyvitamin D was associated with a 26% increased rate of all-cause mortality, as compared to those categorised as having the highest level. Further analysis revealed that the risk for mortality was more evident in those who did not have cardiovascular disease at the beginning of the study compared with those who did.
Click here to view the abstract of the study.
This follows a previous study, published in the same journal, in which data was gathered on 3,258 men and women scheduled for coronary x-rays. Patients were followed up over a period of 7.7 years; low levels of 1,25(OH)2D was found to be independently associated with all-cause and cardiovascular mortality.
The Role Of Supplementation
This research is very exciting but it is not recommended that people supplement high amounts of vitamin D, which is a fat soluble vitamin and as a result can be toxic. Vitamin D toxicity (hypervitaminosis D) induces abnormally high calcium levels (hypercalcemia), which could result in bone loss, kidney stones, and calcification of organs like the heart and kidneys if untreated over a long period of time. It is however vital to ensure good vitamin D intake by combining good amounts of sun exposure (about 45 minutes per week) with a diet that includes oily fish, eggs and some milk. Bear in mind that the application of sunscreen with an SPF factor of 8 reduces production of vitamin D by 95%. Supplementation of up to 10μg (400IU) is safe; intake at this level is recommended for the elderly, who have a reduced capacity to synthesize vitamin D in the skin, and those at risk of deficiency such as Islamic women using the hijab; 5-10μg may also be needed in the winter months among those living in the northern hemisphere who didn't get enough sun in the summer.
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