Sunshine stimulates vitamin D production by the skin
Spending more time in the sun could help older people cut their risk of heart disease and diabetes say experts.
Sun exposure helps the skin make vitamin D - a vitamin older people are generally deficient in due to their lifestyles and ageing processes.
A team at Warwick University has shown a deficiency increases the risk of metabolic syndrome, which is linked to diabetes and cardiovascular disease.
Their study of more than 3,000 people is published in Diabetes Care.
The researchers say older people would benefit from more sunshine, although it is still important to be sensible in the sun as UV damage is linked with skin cancer.
Among the 50 to 70-year-olds living in China that the scientists studied, 94% had a vitamin D (25-hydroxyvitamin D) deficiency or insufficiency and 42% also had metabolic syndrome.
Lead researcher Dr Oscar Franco says the same can be seen in British and American populations too.
"Vitamin D deficiency is becoming a condition that is causing a large burden of disease across the globe with particular deleterious impact among the elderly.
"We found that low vitamin D levels were associated with an increased risk of having metabolic syndrome, and was also significantly associated with increased insulin resistance."
Metabolic syndrome's cluster of obesity, high blood sugar, high blood pressure and high cholesterol can lead to heart disease, stroke and diabetes.
Vitamin D is mainly obtained from exposure to the sun, as well as from certain foods such as oily fish and eggs.
There are concerns that many people, including the elderly, pregnant women and those who wear all-concealing clothing do not get enough of the vitamin.
Dr Franco said there were many factors which could explain why older people had less vitamin D in their blood, including changes in lifestyle factors such as clothing and outdoor activity.
"As we get older our skin is less efficient at forming vitamin D and our diet may also become less varied, with a lower natural vitamin D content.
"When we are older we may need to spend more time outdoors to stimulate the same levels of vitamin D we had when we were younger."
Lorna Layward from Age Concern and Help The Aged said: "We have always advocated that older people get out into the sunshine for a bit each day if they can. A bit of sun is good for you.
"We hear a lot about sun exposure and the risk of cancer, but older people tend to be at the other end of the spectrum. They do not get enough sun and tend to cover up and wear more clothing."
Ed Yong of Cancer Research UK said: "The amount of sunlight it takes to make enough vitamin D is always less than the amounts that cause reddening or burning, so it should be possible to get the benefits of this vitamin without increasing the risk of skin cancer.
"Elderly people can also boost their vitamin D levels by eating foods like oily fish, or by using vitamin D supplements on the advice of their GP."