Scientists say sunshine could be one of the main drivers for making people feel alert and full of life.
Vitamin D, produced in the body through exposure to sunlight, has been found to boost energy levels and make muscles work efficiently.
The hormone made by the skin enhances the activity of mitochondria, the body’s natural batteries.
Getting some sun – when it comes out – could give a boost many people have lacked during the wet weather.
Although vitamin D is present in a healthy diet, around 90 per cent comes from exposure to the sun.
In the diet it is found in fish, fish liver oils, egg yolks and fortified cereals.
The study also found patients with low vitamin D enjoyed an energy boost when their levels were raised with supplements.
Study leader Dr Akash Sinha, from the Newcastle upon Tyne Hospitals NHS Foundation Trust, said vitamin D “significantly” improves muscle function.
He said: “Examining this small group of patients with vitamin D deficiency who experienced symptoms of muscle fatigue, we found that those with very low vitamin D levels improved their muscle efficiency significantly when their vitamin D levels were improved.”
Around 60 per cent of the population are thought to be deficient in vitamin D, particularly children under five, those with dark skin and the elderly.
The vitamin has long been associated with bone health and a lack of it is known to cause rickets, which leads to softening and weakening of the bones.
A deficiency can also lead to muscle fatigue thought to be linked to reduced effectiveness of mitochondria which use glucose and oxygen to make energy.
They produce ATP – a substance which muscle cells use for energy and movement.
Of the patients I see, around 60 per cent are vitamin D deficient
When patients are given vitamin D supplements, scientists found mitochondria recovered more quickly after muscle usage.
Patients also reported feeling less tired and washed out.
Dr Sinha added that in the absence of sunlight, vitamin D tablets could help boost energy levels.
He said: “Of the patients I see, around 60 per cent are vitamin D deficient.”
The report is published in the journal Endocrine Abstracts.