Could be with food, beverages, gadgets, etc.
For me I've found that eating heavily salted meat, taking a source of iodine (usually as whole seaweed), doing bodily mobility work, or Wim Hof breathing are all things that noticeably improve my feeling of bodily warmth quickly.
Not sure why the study considers January to May to be winter months, but this is yet another study that links maternal metabolism (and serotonin) to autism. The official explanation is increased flu infection and lower vitamin D levels in the winter. While these may be contributing factors, I...